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  As Of               Filer                 Filing     As/For/On Docs:Pgs              Issuer               Agent

 2/10/05  Exelon Corp                       S-4                   10:326                                    Merrill Corp/New/- FA

Document/Exhibit                   Description                      Pages   Size 

 1: S-4         Registration of Securities Issued in a              HTML  2,352K 
                          Business-Combination Transaction                       
 2: EX-8.1      Opinion re: Tax Matters                                3     16K 
 3: EX-8.2      Opinion re: Tax Matters                                3     17K 
 4: EX-23.1     Consent of Experts or Counsel                          1      7K 
 5: EX-23.2     Consent of Experts or Counsel                          1      7K 
 6: EX-99.1     Miscellaneous Exhibit                                  2     12K 
 7: EX-99.2     Miscellaneous Exhibit                                  2     16K 
 8: EX-99.3     Miscellaneous Exhibit                                  1      7K 
 9: EX-99.4     Miscellaneous Exhibit                                  1      8K 
10: EX-99.5     Miscellaneous Exhibit                                  1      8K 

As filed with the Securities and Exchange Commission on February 10, 2005

Registration No. 333-          

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

Form S-4
REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

Exelon Corporation
(Exact name of registrant as specified in its charter)

10 South Dearborn Street
37th Floor
Chicago, Illinois 60680-5379
(312) 394-7398
(Address, including zip code, and telephone number, including area code, of registrant's principal executive offices)

Randall E. Mehrberg, Esq.
Exelon Corporation
10 South Dearborn Street
37th Floor
Chicago, Illinois 60680-5379
(312) 394-7398
(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies To:

        Approximate date of commencement of proposed sale of the securities to the public:    As soon as practicable after this registration statement becomes effective and after the conditions to the completion of the proposed transaction described in the joint proxy statement/prospectus have been satisfied or waived.

        If the securities being registered on this form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, check the following box.    o

        If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

        If this form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

CALCULATION OF REGISTRATION FEE

(1)

The number of shares of the registrant being registered is based upon an estimate of (x) the maximum number of shares of common stock, no par value per share, of Public Service Enterprise Group Incorporated ("PSEG Common Stock") presently outstanding or issuable or expected to be issued in connection with the merger of Public Service Enterprise Group Incorporated into the registrant multiplied by (y) the exchange ratio of 1.225 shares of common stock, no par value per share, of the registrant for each share of PSEG Common Stock.

(2)

Calculated by multiplying the estimated aggregate offering price of the securities to be registered by 0.00011770.

        The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

The Information in this joint proxy statement/prospectus is not complete and may be changed. These securities may not be sold until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary joint proxy statement/prospectus is not an offer to sell and it is not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

PRELIMINARY COPY—SUBJECT TO COMPLETION, DATED FEBRUARY 10, 2005

MERGER PROPOSAL—YOUR VOTE IS IMPORTANT

        On behalf of the boards of directors and management of both Exelon Corporation and Public Service Enterprise Group Incorporated, we are pleased to deliver our joint proxy statement/prospectus for the merger involving Exelon and PSEG. We believe this merger will create a strong combined company that will deliver important benefits to our shareholders, to our customers and to the communities we serve.

        If the merger is completed, PSEG shareholders will receive 1.225 shares of Exelon common stock for each share of PSEG common stock held. The exchange ratio is fixed and will not be adjusted to reflect stock price changes prior to the completion of the merger. Based on the closing price of Exelon common stock on the New York Stock Exchange on December 15, 2004, the last full trading day prior to a significant increase in trading volume from the average trading volume of Exelon and PSEG common stock and inquiries from The Wall Street Journal regarding whether Exelon and PSEG were in advanced merger discussions, the exchange ratio represented approximately $53.14 in value for each share of PSEG common stock. Based on the closing price of Exelon common stock on the New York Stock Exchange on December 16, 2004, the last full trading day prior to the publication of news articles reporting that Exelon and PSEG were in advanced merger discussions, the exchange ratio represented approximately $52.19 in value for each share of PSEG common stock. Based on the closing price of Exelon common stock on the New York Stock Exchange on December 17, 2004, the last full trading day prior to our public announcement of the merger, the exchange ratio represented approximately $51.28 in value for each share of PSEG common stock. Based on the closing price of Exelon common stock on the New York Stock Exchange on [    •    ], 2005, of $[    •    ], the exchange ratio represented approximately $[    •    ] in value for each share of PSEG common stock. The value of the consideration to be received by PSEG shareholders will fluctuate with changes in the price of Exelon common stock. We urge you to obtain current market quotations for Exelon and PSEG common stock.

        Exelon shareholders will continue to own their existing Exelon shares. We estimate that Exelon may issue up to approximately [    •    ] million shares of Exelon common stock to PSEG shareholders as contemplated by the merger agreement, which includes approximately [    •    ] million shares of Exelon common stock issuable pursuant to PSEG stock options to be assumed by Exelon and substituted with options to purchase Exelon common stock. Upon completion of the merger, Exelon's shareholders immediately prior to the merger will own approximately [    •    ]% of Exelon's outstanding shares on a fully diluted basis and former PSEG shareholders will own approximately [    •    ]% of Exelon's outstanding common stock on a fully diluted basis. Upon completion of the merger, Exelon will change its name from Exelon Corporation to Exelon Electric & Gas Corporation. Exelon common stock will continue to be listed on the New York Stock Exchange.

        For a discussion of the United States federal income tax consequences of the merger, see "The Merger—Material United States Federal Income Tax Consequences of the Merger" beginning on page [    •    ] of this joint proxy statement/prospectus.

        We urge you to read this joint proxy statement/prospectus, which includes important information about the merger and our annual meetings. In particular, see the section titled "Risk Factors" on pages [    •    ] through [    •    ] of this joint proxy statement/prospectus which contains a description of the risks that you should consider in evaluating the merger.

        Exelon asks that, in addition to the other matters to be considered at the Exelon annual meeting, Exelon shareholders approve the issuance of shares of Exelon common stock as contemplated by the merger agreement. Exelon's annual meeting will be held at the following time and place:

        [    •    ], 2005
[    •    ] local time
[Location TBD]

        Exelon's board of directors has reviewed and considered the terms of the merger and the merger agreement and has unanimously determined that the merger, including the issuance of shares of Exelon common stock as contemplated by the merger agreement, is advisable, fair to and in the best interests of Exelon and its shareholders and unanimously recommends that Exelon shareholders vote FOR the proposal to approve the issuance of shares of Exelon common stock as contemplated by the merger agreement.

        PSEG asks that, in addition to the other matters to be considered at the PSEG annual meeting, PSEG shareholders approve the merger agreement and thereby approve the merger. PSEG's annual meeting will be held at the following time and place:

        [    •    ], 2005
[    •    ] local time
[Location TBD]

        PSEG's board of directors has reviewed and considered the terms of the merger and the merger agreement and has unanimously determined that the merger is advisable, fair to and in the best interests of PSEG and its shareholders and unanimously recommends that PSEG shareholders vote FOR the proposal to approve the merger agreement and thereby approve the merger.

        We cannot complete the merger unless the Exelon shareholders approve the issuance of shares of Exelon common stock as contemplated by the merger agreement and the PSEG shareholders approve the merger agreement. Your vote is important.

        Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved the securities to be issued under this joint proxy statement/prospectus or determined if this joint proxy statement/prospectus is accurate or adequate. Any representation to the contrary is a criminal offense.

        This joint proxy statement/prospectus is dated [    •    ], 2005 and is first being mailed to Exelon and PSEG shareholders on or about [    •    ], 2005.

REFERENCES TO ADDITIONAL INFORMATION

        This joint proxy statement/prospectus incorporates important business and financial information about Exelon and PSEG from other documents that are not included in or delivered with this joint proxy statement/prospectus. This information is available to you without charge upon your written or oral request. You can obtain copies of the documents incorporated by reference into this joint proxy statement/prospectus through the Securities and Exchange Commission website at www.sec.gov or by requesting them in writing or by telephone from the appropriate company at the following addresses and telephone numbers:

         If you would like to request documents, please do so by [    •    ], 2005, in order to receive them before your annual meeting.

        See "Where You Can Find More Information" beginning on page [    •    ] of this joint proxy statement/prospectus.

VOTING BY TELEPHONE, BY THE INTERNET OR BY MAIL

        Exelon shareholders of record may submit their proxies:

•

by telephone, by calling the toll-free number (877) 779-8683 in the United States, Canada or Puerto Rico on a touch-tone phone and following the recorded instructions;



•

by accessing the Internet website at www.eproxyvote.com/exc and following the instructions on the website; or



•

by mail, by indicating your voting preference on the proposals on each proxy card you receive, signing and dating each proxy card and returning each proxy card in the prepaid envelope that accompanied that proxy card.

        PSEG shareholders of record may submit their proxies:

•

by telephone, by calling the toll-free number (866) 242-0618 in the United States, Canada or Puerto Rico on a touch-tone phone and following the recorded instructions;



•

by accessing the Internet website at www.proxyvotenow.com/pseg and following the instructions on the website; or



•

by mail, by indicating your voting preference on the proposals on each proxy card you receive, signing and dating each proxy card and returning each proxy card in the prepaid envelope that accompanied that proxy card.

        If you hold your shares through a bank, broker, custodian or other recordholder, please refer to your proxy card or voter information form or the information forwarded by your bank, broker, custodian or other recordholder to see which options are available to you.

NOTICE OF ANNUAL MEETING OF SHAREHOLDERS
OF EXELON CORPORATION

TO THE SHAREHOLDERS OF EXELON CORPORATION:

        Exelon will hold the annual meeting of Exelon shareholders on [    •    ], 2005, at [    •    ] local time, at [    •    ].

        The purpose of the annual meeting is to consider and take action on the following:

        1.     A proposal to approve the issuance of shares of Exelon common stock as contemplated by the Agreement and Plan of Merger, dated as of December 20, 2004, between Exelon Corporation and Public Service Enterprise Group Incorporated. A copy of the merger agreement is attached as Annex A to the joint proxy statement/prospectus accompanying this notice. In the merger, each share of PSEG common stock outstanding immediately prior to completion of the merger will be converted into the right to receive 1.225 shares of Exelon common stock.

        2.     The election of five Class II directors: Edward A. Brennan, Bruce DeMars, Nelson A. Diaz, John W. Rowe and Ronald Rubin, each for a term of three years.

        3.     A proposal to approve an amendment to Exelon's Amended and Restated Articles of Incorporation to increase the number of authorized shares of Exelon common stock from 1,200,000,000 to 2,000,000,000.

        4.     A proposal to ratify PricewaterhouseCoopers LLP as Exelon's independent accountants for the year 2005.

        5.     A proposal to approve the Exelon Corporation 2006 Long-Term Incentive Plan.

        6.     A proposal to approve the Exelon Corporation Employee Stock Purchase Plan for Unincorporated Subsidiaries.

        7.     Any proposal of the Exelon board of directors to adjourn or postpone the annual meeting.

        8.     Any other business that properly comes before the annual meeting and any adjournment or postponement thereof.

        Shareholders of record of Exelon common stock at the close of business on [    •    ], 2005 will be entitled to vote at the annual meeting and any adjournment or postponement of that meeting. As of the record date, there were [    •    ] shares of Exelon common stock outstanding. Each share of common stock is entitled to one vote on each matter properly brought before the meeting.

        You are cordially invited to attend the meeting; however, whether or not you expect to attend in person, you can be sure your shares are represented at the meeting by promptly voting and submitting your proxy by phone, by Internet or by completing, signing, dating and returning the enclosed proxy in the enclosed prepaid envelope.

        If you plan on attending the annual meeting, please bring your admission ticket and a photo ID along with you. The stub of your proxy card or voter information form will serve as your admission ticket.

        Your board of directors unanimously recommends that you vote for the proposal to approve the issuance of shares of Exelon common stock as contemplated by the merger agreement, which is described in detail in the joint proxy statement/prospectus accompanying this notice, and for proposals two through seven in this notice.

By Order of the Board of Directors
 
Katherine K. Combs
Vice President, Corporate Secretary
and Deputy General Counsel

YOUR VOTE IS IMPORTANT

        WE URGE YOU TO VOTE YOUR SHARES AS PROMPTLY AS POSSIBLE BY (1) CALLING THE TOLL-FREE NUMBER (877) 779-8683, (2) ACCESSING THE INTERNET WEBSITE AT www.eproxyvote.com/exc OR (3) COMPLETING, SIGNING, DATING AND MAILING THE ENCLOSED PROXY CARD.

Public Service Enterprise Group Incorporated
80 Park Plaza, P.O. Box 1171
Newark, New Jersey 07101-1171

NOTICE OF ANNUAL MEETING OF SHAREHOLDERS
OF PUBLIC SERVICE ENTERPRISE GROUP INCORPORATED

TO THE SHAREHOLDERS OF PUBLIC SERVICE ENTERPRISE GROUP INCORPORATED:

        PSEG will hold the annual meeting of PSEG shareholders on [    •    ], 2005, at [    •    ] local time, at [    •    ].

        The purpose of the annual meeting is to consider and take action on the following:

        1.     A proposal to approve the Agreement and Plan of Merger, dated as of December 20, 2004, between Exelon Corporation and Public Service Enterprise Group Incorporated. A copy of the merger agreement is attached as Annex A to the joint proxy statement/prospectus accompanying this notice. In the merger, each share of PSEG common stock outstanding immediately prior to completion of the merger will be converted into the right to receive 1.225 shares of Exelon common stock.

        2.     To elect three members of Class III of the PSEG board of directors: Conrad K. Harper, Shirley Ann Jackson and Thomas A. Renyi.

        3.     To consider and act upon the ratification of the appointment of Deloitte & Touche LLP as PSEG's independent auditor for the year 2005.

        4.     To consider and act upon any proposal by the PSEG board of directors to adjourn or postpone the PSEG annual meeting.

        5.     To consider and act upon a shareholder proposal related to executive compensation, if presented at the meeting.

        6.     Any other business that properly comes before the annual meeting and any adjournment or postponement thereof.

        Shareholders of record of PSEG common stock at the close of business on [    •    ], 2005 will be entitled to vote at the annual meeting and any adjournment or postponement of that meeting. As of the record date, there were [    •    ] shares of PSEG common stock outstanding. Each share of common stock is entitled to one vote on each matter properly brought before the meeting, except for the proposal relating to the election of directors, on which PSEG shareholders are entitled to cumulative voting.

        You are cordially invited to attend the meeting; however, whether or not you expect to attend in person, you can be sure your shares are represented at the meeting by promptly voting and submitting your proxy by phone, by Internet or by completing, signing, dating and returning the enclosed proxy in the enclosed prepaid envelope.

        If you plan on attending the annual meeting, please bring your admission ticket and a photo ID along with you. The portion of your proxy card or voter information form marked "Admission Ticket" will serve as your admission ticket.

        Your board of directors unanimously recommends that you vote for the proposal to approve the merger agreement and thereby approve the merger, which is described in detail in the joint proxy statement/prospectus accompanying this notice, and for proposals two through four in this notice and against proposal five in this notice.

YOUR VOTE IS IMPORTANT
 


        WE URGE YOU TO VOTE YOUR SHARES AS PROMPTLY AS POSSIBLE BY (1) CALLING THE TOLL-FREE NUMBER (866) 242-0618, (2) ACCESSING THE INTERNET WEBSITE AT www.proxyvotenow.com/pseg OR (3) COMPLETING, SIGNING, DATING AND MAILING THE ENCLOSED PROXY CARD.

        PLEASE DO NOT SEND YOUR COMMON STOCK CERTIFICATES AT THIS TIME. IF THE MERGER IS COMPLETED, YOU WILL BE SENT INSTRUCTIONS REGARDING THE SURRENDER OF YOUR CERTIFICATES.

    TABLE OF CONTENTS

i

ii

iii

   
CHAPTER ONE
THE INTRODUCTION

QUESTIONS AND ANSWERS ABOUT THE ANNUAL MEETINGS

Q:

Why am I receiving this document?

A:

We are delivering this document to you because it is serving as both a joint proxy statement of Exelon and PSEG and a prospectus of Exelon. It is a joint proxy statement because it is being used by our boards of directors to solicit proxies of our shareholders. It is a prospectus because Exelon is offering shares of its common stock in exchange for shares of PSEG common stock if the merger is completed.

Q:

What do I need to do now?

A:

After you carefully read this joint proxy statement/prospectus, please respond by submitting your proxy by telephone or the Internet or by completing, signing, dating and returning your signed proxy card(s) in the enclosed prepaid return envelope, as soon as possible, so that your shares may be represented at your annual meeting. In order to assure that your vote is recorded, please vote your proxy as instructed on your proxy card even if you currently plan to attend your annual meeting in person.

Q:

Why is my vote important?

A:

Exelon shareholders are being asked to approve the issuance of shares of Exelon common stock as contemplated by the merger agreement and to take action on the other proposals in the Exelon notice. PSEG shareholders are being asked to approve the merger agreement and thereby approve the merger and to take action on the other proposals in the PSEG notice. If you do not submit your proxy by telephone or the Internet, or return your signed proxy card(s) by mail or vote in person at your annual meeting, it will be more difficult for Exelon and PSEG to obtain the necessary quorum to hold their respective annual meetings.

Q:

How will my proxy be voted?

A:

If you vote by telephone or by the Internet or by completing, signing, dating and returning your signed proxy card(s), your proxy will be voted in accordance with your instructions.

If you are an Exelon shareholder of record and submit your proxy but do not indicate how you want to vote, your shares will be voted FOR the proposal to approve the issuance of shares of Exelon common stock as contemplated by the merger agreement, FOR the proposal to elect the directors named in the director proposal, FOR the proposal to approve the amendment to Exelon's Amended and Restated Articles of Incorporation to increase the number of authorized shares of Exelon common stock, FOR the proposal to ratify PricewaterhouseCoopers LLP as Exelon's independent accountants, FOR the proposal to approve the Exelon Corporation 2006 Long-Term Incentive Plan, FOR the proposal to approve the Exelon Corporation Employee Stock Purchase Plan for Unincorporated Subsidiaries and FOR the adjournment or postponement of the annual meeting, if necessary.

If you are a PSEG shareholder of record and submit your proxy but do not indicate how you want to vote, your shares will be voted FOR the proposal to approve the merger agreement, FOR the proposal to elect the directors named in the director proposal, FOR the proposal to ratify Deloitte & Touche LLP as PSEG's independent auditor, FOR the adjournment or postponement of the annual meeting, if necessary, and AGAINST the shareholder proposal.

1

Q:

May I vote in person?

A:

Yes. If you are a shareholder of record of Exelon common stock as of [    •    ], 2005 or of PSEG common stock as of [    •    ], 2005, you may attend your annual meeting and vote your shares in person, instead of submitting your proxy by telephone or by the Internet or returning your signed proxy card(s).

Q:

If my shares are held in "street name" by my broker, will my broker vote my shares for me?

A:

If you are an Exelon shareholder whose shares are held in "street name" by your broker, you must provide your broker with instructions on how to vote your shares; otherwise, your broker will not vote your shares on the proposal to approve the issuance of shares of Exelon common stock as contemplated by the merger agreement, the proposal to approve the amendment to Exelon's Amended and Restated Articles of Incorporation to increase the number of authorized shares of Exelon common stock, the proposal to approve the Exelon Corporation 2006 Long-Term Incentive Plan or the proposal to approve the Exelon Corporation Employee Stock Purchase Plan for Unincorporated Subsidiaries.

If you are a PSEG shareholder whose shares are held in "street name" by your broker, you must provide your broker with instructions on how to vote your shares; otherwise, your broker will not vote your shares on the proposal to approve the merger agreement or the shareholder proposal.

You should be sure to provide your broker with instructions on how to vote your shares. Please check the voting form used by your broker to see if it offers telephone or Internet submission of proxies.

Q:

What if I fail to instruct my broker?

A:

If you fail to instruct your broker to vote your shares and the broker submits an unvoted proxy, the resulting broker "non-vote" will, in the circumstances described under "Chapter Two—Information About the Annual Meetings and Voting," be counted toward a quorum at your annual meeting but will not be counted in determining the number of votes cast with respect to a proposal.

Q:

Who will count the vote?

A:

For the Exelon proposals, representatives of Equiserve Trust Company, N.A. and Exelon's Office of the Corporate Secretary will count the votes and serve as judges of election.

For the PSEG proposals, representatives of Corporate Election Services, Inc. will count the vote and serve as inspectors of election.

Q:

What does it mean if I receive more than one set of materials?

A:

This means you own shares of both Exelon and PSEG or you own shares of Exelon or PSEG that are registered under different names. For example, you may own some shares directly as a shareholder of record and other shares through a broker or you may own shares through more than one broker. In these situations, you will receive multiple sets of proxy materials. It is necessary for you to vote, sign and return all of the proxy cards or follow the instructions for any alternative voting procedure on each of the proxy cards you receive in order to vote all of the shares you own. Each proxy card you receive will come with its own prepaid return envelope; if you vote by mail, make sure you return each proxy card in the return envelope which accompanied that proxy card.

2

Q:

Can I revoke my proxy and change my vote?

A:

Yes. You have the right to revoke your proxy at any time prior to the time your shares are voted at your annual meeting. If you are a shareholder of record, your proxy can be revoked in several ways:

•

by entering a new vote by telephone or the Internet;

•

by delivering a written revocation to your company's secretary that is received prior to your annual meeting;

•

by submitting another valid proxy bearing a later date that is received prior to your annual meeting; or

•

by attending your annual meeting and voting your shares in person.

However, if your shares are held in "street name" through a bank, broker, custodian or other recordholder, you must check with your bank, broker, custodian or other recordholder to determine how to revoke your proxy.

Q:

When and where are the annual meetings?

A:

The Exelon annual meeting will take place on [    •    ], 2005, at [    •    ] local time, at [    •    ].

The PSEG annual meeting will take place on [    •    ], 2005, at [    •    ] local time, at [    •    ].

Q:

What must I bring to attend the annual meetings?

A:

Admittance to the annual meetings is limited to shareholders of Exelon or PSEG, as the case may be, who are eligible to vote or their authorized representatives. If you wish to attend the meeting, bring the portion of your proxy which is marked as your "Admission Ticket" or your voter information form. Also, be sure to bring a photo ID. Seating is limited.

Q:

Should I send in my stock certificates now?

A:

No. After the merger is completed, Exelon will send PSEG shareholders written instructions for exchanging their PSEG stock certificates for Exelon stock certificates. Exelon shareholders will keep their existing stock certificates.

Q:

Are there risks I, as an Exelon shareholder, should consider in deciding to vote on the issuance of shares of Exelon common stock as contemplated by the merger agreement or, as a PSEG shareholder, should consider in deciding to vote on the approval of the merger agreement?

A:

Yes, in evaluating the issuance of shares of Exelon common stock as contemplated by the merger agreement, or the merger agreement and the merger, you should carefully read this joint proxy statement/prospectus, including the factors discussed in the section titled "Risk Factors" beginning on page [    •    ] of this joint proxy statement/prospectus.

Q:

Who can answer any questions I may have about the annual meetings or the merger?

A:

Exelon shareholders may call Georgeson Shareholder Communications Inc. at [    •    ].

PSEG shareholders may call Morrow & Co., Inc. at [    •    ].

3

   
SUMMARY

        This summary highlights selected information from this joint proxy statement/prospectus related to the merger and may not contain all of the information that is important to you. To understand the merger fully and for a more complete description of the legal terms of the merger agreement, you should carefully read this entire joint proxy statement/prospectus and the documents to which this joint proxy statement/prospectus refers you. A copy of the merger agreement is attached as Annex A to this joint proxy statement/prospectus and is incorporated by reference into this joint proxy statement/prospectus. See "Where You Can Find More Information" on page [    •    ] of this joint proxy statement/prospectus.

The Companies Involved in the Merger (see page [    •    ])

Exelon Corporation
10 South Dearborn Street—37th Floor
P.O. Box 805379
Chicago, Illinois 60680-5379
(312) 394-7398
Internet address: www.exeloncorp.com

        Exelon Corporation, a registered public utility holding company under the Public Utility Holding Company Act of 1935, as amended, through its subsidiaries, operates in three business segments—Energy Delivery, Generation and Enterprises—as described below. In addition to Exelon's three business segments, Exelon Business Services Company, a subsidiary of Exelon, provides Exelon and its subsidiaries with financial, human resource, legal, information technology, supply management and corporate governance services.

        Energy Delivery.    Exelon's energy delivery business consists of the purchase and sale of electricity and distribution and transmission services by Commonwealth Edison Company in northern Illinois, including the City of Chicago, and by PECO Energy Company in southeastern Pennsylvania, including the City of Philadelphia, and the purchase and sale of natural gas and distribution services by PECO in the Pennsylvania counties surrounding the City of Philadelphia.

        Generation.    Exelon's generation business consists of the owned and contracted for electric generating facilities and energy marketing operations of Exelon Generation Company, LLC, a 49.5% interest in two power stations in Mexico and the competitive retail sales business of Exelon Energy Company.

        Enterprises.    Exelon's enterprises business is comprised of infrastructure and electrical contracting services of Exelon Enterprises Company, LLC and other investments weighted towards the communications and energy services industries. During 2004 and 2003, Enterprises exited a significant number of businesses and investments. Exelon plans to divest or wind-down the remaining assets of Enterprises during 2005.

        Exelon was incorporated in Pennsylvania in February 1999.

Public Service Enterprise Group Incorporated
80 Park Plaza
P.O. Box 1171
Newark, New Jersey 07101-1171
(973) 430-7000
Internet address: www.pseg.com

        Public Service Enterprise Group Incorporated is an exempt public utility holding company under PUHCA. PSEG has four principal direct wholly-owned subsidiaries: Public Service Electric and Gas

4

Company, PSEG Power LLC, PSEG Energy Holdings LLC and PSEG Services Corporation. PSEG was incorporated under the laws of the State of New Jersey in 1985.

        PSE&G.    PSE&G is an operating public utility company engaged principally in the transmission and distribution of electric energy and gas service in New Jersey.

        PSEG Power.    PSEG Power is a multi-regional, wholesale energy supply company that integrates its generating asset operations with its wholesale energy, fuel supply, energy trading and marketing and risk management function through three principal direct wholly-owned subsidiaries: PSEG Nuclear LLC, PSEG Fossil LLC and PSEG Energy Resources & Trade LLC.

        PSEG Energy Holdings.    PSEG Energy Holdings has two principal direct wholly-owned subsidiaries, PSEG Global LLC and PSEG Resources LLC. PSEG Global has pursued investment opportunities in electric generation, transmission and distribution facilities and is engaged in power production and distribution in selected domestic and international markets. PSEG Resources invests in energy-related financial transactions and manages a diversified portfolio of assets. Upon completion of the merger, the combined company intends to pursue opportunities to sell certain of PSEG Global's investments that do not meet the strategic objectives of the combined company.

        PSEG Services.    PSEG Services provides management and administrative services to PSEG and its subsidiaries.

The Merger (see page [    •    ])

        Under the terms of the merger, PSEG will merge with and into Exelon with Exelon continuing as the surviving corporation. Upon completion of the merger, Exelon will change its name to Exelon Electric & Gas Corporation.

        The merger agreement is attached as Annex A to this joint proxy statement/prospectus. We urge you to read the merger agreement carefully and fully, as it is the legal document that governs the merger.

PSEG Shareholders Will Receive 1.225 Shares of Exelon Common Stock for Each Share of PSEG Common Stock (see page [    •    ])

        Subject to the terms and conditions of the merger agreement, upon completion of the merger, PSEG shareholders will receive 1.225 shares of Exelon common stock for each share of PSEG common stock they hold. Exelon will not issue fractional shares pursuant to the merger. As a result, the total number of shares of Exelon common stock that each PSEG shareholder would otherwise receive pursuant to the merger will be rounded down to the nearest whole number, and each PSEG shareholder will receive such whole number of shares of Exelon common stock and a cash payment for the remaining fraction of a share of Exelon common stock that such shareholder would otherwise receive, if any, based on the last reported sale price per share of Exelon common stock at the close of business on the closing date of the merger, rounded down to the nearest cent.

        Example: If you own 137 shares of PSEG common stock when the merger is completed, you will be entitled to receive 167 shares of Exelon common stock and a check for the market value of 0.83 shares of Exelon common stock at the close of business on the closing date of the merger.

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Each Outstanding Option to Purchase PSEG Common Stock and Each PSEG Equity-Based Award Will be Substituted with an Option to Purchase Shares of Exelon Common Stock or an Exelon Equity-Based Award at the Exchange Ratio and All Restrictions on PSEG Equity-Based Awards Will Be Assigned to Exelon (see page [    •    ])

        Upon completion of the merger, each outstanding option to purchase shares of PSEG common stock will be assumed by Exelon and substituted with an option to purchase shares of Exelon common stock, exercisable on generally the same terms and conditions that applied before the merger. The number of shares of Exelon common stock subject to the substitute Exelon stock option will equal the number of shares of PSEG common stock subject to the PSEG stock option immediately prior to completion of the merger, multiplied by the exchange ratio, rounded down to the nearest whole share. The per share exercise price of each substitute Exelon stock option will equal the exercise price of the PSEG stock option immediately prior to completion of the merger divided by the exchange ratio, rounded up to the nearest whole cent. In addition, upon completion of the merger, Exelon will assume all PSEG equity-based awards and substitute them with equity-based awards with respect to shares of Exelon common stock on generally the same terms and conditions that applied before completion of the merger. The number of shares of Exelon common stock issuable under those awards, and the exercise prices for those awards, will be adjusted to take into account the exchange ratio.

        Upon completion of the merger, all restrictions on PSEG equity-based awards immediately prior to completion of the merger, including all repurchase and forfeiture rights, will be assigned to Exelon, and subject to any acceleration, lapse or other vesting occurring by operation of the merger, those PSEG equity-based awards will continue to be unvested and subject to the same restrictions which applied immediately prior to completion of the merger.

The Exchange Ratio is Fixed and Will Not Be Adjusted in Response to Changes in Our Stock Prices (see page [    •    ])

        The exchange ratio is fixed in the merger agreement and neither Exelon nor PSEG has the right to terminate the merger agreement based solely on changes in either party's stock price. The market value of the Exelon common stock that PSEG shareholders receive in the merger may fluctuate significantly from its current value.

        The table below shows the closing prices of Exelon and PSEG common stock, which are listed on the New York Stock Exchange under the trading symbols "EXC" and "PEG," respectively, and the pro forma "equivalent stock price" at the close of the regular trading session on:

•

December 15, 2004, the last full trading day prior to a significant increase in trading volume from the average trading volume of Exelon and PSEG common stock and inquiries from The Wall Street Journal regarding whether Exelon and PSEG were in advanced merger discussions;



•

December 16, 2004, the last full trading day prior to the publication of news articles reporting that Exelon and PSEG were in advanced merger discussions;



•

December 17, 2004, the last full trading day prior to our public announcement of the merger; and



•

[    •    ], 2005, the most recent trading day for which that information was available prior to the mailing of this joint proxy statement/prospectus.

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        The "equivalent stock price" of shares of PSEG common stock represents the closing price per share of Exelon common stock on the New York Stock Exchange as of the applicable date, multiplied by the exchange ratio of 1.225.

        The value of the consideration to be received by PSEG shareholders will fluctuate with changes in the price of Exelon common stock. You are urged to obtain current market quotations for shares of both companies.

Exelon and PSEG Expect to Continue Their Respective Stated Dividend Policies Until Completion of the Merger; Exelon has Agreed, Subject to Specified Limitations, to Increase its Dividend Following Completion of the Merger to Equal PSEG's Dividend on an Exchange Ratio Adjusted Basis

        The merger agreement permits each of us to continue to pay regular dividends to our respective shareholders in accordance with our previously announced dividend policies. Exelon has previously indicated it expects to maintain a dividend payout policy of 50% to 60% of earnings. On January 25, 2005, Exelon declared a first quarter dividend for 2005 of $0.40 per share. PSEG has announced that it will increase its first quarter dividend for 2005 to $0.56 per share from $0.55 per share, for an indicated annual dividend increase of $0.04 per share for the year 2005. For the year 2006, PSEG will continue to evaluate its dividend payment and consider modest increases.

        We have agreed to coordinate dividend declarations and the related record dates and payment dates so that our shareholders will not receive two dividends, or fail to receive one dividend, for any single calendar quarter. Accordingly, prior to completion of the merger, we may coordinate and amend our record dates and payment dates in order to effect this policy.

        In addition, the merger agreement provides that, subject to applicable law and the fiduciary duties of its board of directors, Exelon will increase its first quarterly dividend paid after completion of the merger to an amount equal, on an exchange ratio adjusted basis, to the dividend PSEG shareholders received in the quarter immediately prior to completion of the merger, up to a maximum of $0.47 per share of Exelon common stock. The lesser of $0.47 and the amount required to equal PSEG's dividend on an exchange ratio adjusted basis is referred to in this joint proxy statement/prospectus as the "threshold amount." If the first quarterly dividend to be paid by Exelon after completion of the merger will be less than the threshold amount, PSEG may make a one time special cash dividend to its shareholders equal to the amount of the difference between the dividend Exelon has informed PSEG it will pay and the threshold amount, on an exchange ratio adjusted basis.

PSEG Shareholders Will Not Recognize Any Gain or Loss for United States Federal Income Tax Purposes Upon the Exchange of Their Shares of PSEG Common Stock, Except that Gain or Loss Will be Recognized on the Receipt of Cash in Lieu of a Fractional Share of Exelon Common Stock (see page [    •    ])

        Each of Sidley Austin Brown & Wood LLP, legal counsel to Exelon, and Pillsbury Winthrop LLP, legal counsel to PSEG, has delivered its opinion that the merger will be treated for United States federal income tax purposes as a "reorganization" within the meaning of Section 368(a) of the Internal Revenue Code of 1986, as amended, and that each of Exelon and PSEG will be a party to the reorganization within the meaning of Section 368(b) of the Internal Revenue Code.

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        Assuming that the foregoing opinions are correct, a holder of shares of PSEG common stock will not recognize any gain or loss upon the exchange of the holder's shares of PSEG common stock for shares of Exelon common stock pursuant to the merger, except that gain or loss will be recognized on the receipt of cash in lieu of a fractional share of Exelon common stock.

        You should read carefully the discussion under the heading "The Merger—Material United States Federal Income Tax Consequences of the Merger" beginning on page [    •    ] of this joint proxy statement/prospectus. The United States federal income tax consequences described above may not apply to some holders of shares of PSEG common stock, including some types of holders specifically referred to on page [    •    ] of this joint proxy statement/prospectus.

        It is a condition to the obligation of each of Exelon and PSEG to complete the merger that, at the closing of the merger, it receive a separate opinion of Sidley Austin Brown & Wood LLP and Pillsbury Winthrop LLP, respectively (or, in either case, another law firm of national standing), substantially to the same effect as the opinions described above. Neither Exelon nor PSEG intends to waive this condition.

        Holders of shares of PSEG common stock are urged to consult their tax advisors as to the specific tax consequences to them of the merger, including the applicability and effect of United States federal, state, local and foreign income and other tax laws in light of their particular circumstances.

Exelon's Financial Advisors Delivered their Opinions to the Exelon Board of Directors to the Effect that, as of December 20, 2004, the Exchange Ratio in the Merger Was Fair, from a Financial Point of View, to Exelon (see page [    •    ])

        Each of Exelon's financial advisors, J.P. Morgan Securities Inc. and Lehman Brothers Inc., has delivered its opinion dated as of December 20, 2004 to the Exelon board of directors that, as of that date, based upon and subject to the assumptions, qualifications and limitations set forth in their respective opinions, the exchange ratio in the merger was fair, from a financial point of view, to Exelon. The full text of the opinions of JPMorgan and Lehman Brothers are attached as Annex B and Annex C, respectively, to this joint proxy statement/prospectus. Exelon urges its shareholders to read the opinions in their entirety. Each of JPMorgan and Lehman Brothers has provided its opinion for the information and assistance of the Exelon board of directors in connection with its consideration of the merger agreement, the issuance of shares of Exelon common stock as contemplated by the merger agreement and the merger, and the opinions do not constitute a recommendation as to how any holder of Exelon common stock should vote with respect to the issuance of shares of Exelon common stock as contemplated by the merger agreement.

        The opinion of each of JPMorgan and Lehman Brothers will not reflect any developments that may occur or may have occurred after the date of the opinions and prior to completion of the merger.

        Pursuant to an engagement letter dated October 26, 2004, Exelon has agreed to pay JPMorgan a fee of $15 million in consideration for its services as financial advisor, $5 million of which was paid following the public announcement of the execution of the merger agreement, $5 million of which is payable upon approval of the issuance of shares of Exelon common stock as contemplated by the merger agreement by Exelon shareholders and $5 million of which is payable upon completion of the merger. Pursuant to an engagement letter dated November 5, 2004, Exelon has agreed to pay Lehman Brothers a fee of $15 million in consideration for its services as financial advisor, $5 million of which was due upon the public announcement of the execution of the merger agreement, $5 million of which is payable upon approval of the issuance of shares of Exelon common stock as contemplated by the merger agreement by Exelon shareholders and $5 million of which is payable upon completion of the merger.

8

PSEG's Financial Advisor Delivered its Opinion to the PSEG Board of Directors to the Effect that, as of December 20, 2004, the Exchange Ratio Under the Merger Agreement Was Fair, from a Financial Point of View, to the Holders of PSEG Common Stock (see page [    •    ])

        PSEG's financial advisor, Morgan Stanley & Co. Incorporated, has delivered its opinion dated as of December 20, 2004 to the PSEG board of directors that, as of that date, based upon and subject to the assumptions, qualifications and limitations discussed in its opinion, the exchange ratio under the merger agreement was fair, from a financial point of view, to the holders of PSEG common stock. The full text of Morgan Stanley's opinion is attached as Annex D to this joint proxy statement/prospectus. PSEG urges its shareholders to read that opinion in its entirety. Morgan Stanley provided its opinion for the information and assistance of the PSEG board of directors in connection with its consideration of the merger agreement and the merger, and the opinion does not constitute a recommendation as to how any holder of PSEG common stock should vote with respect to the merger agreement.

        The opinion of Morgan Stanley will not reflect any developments that may occur or may have occurred after the date of its opinion and prior to completion of the merger.

        Pursuant to an engagement letter dated November 8, 2004, PSEG has agreed to pay Morgan Stanley a fee of $20 million in consideration for its services as financial advisor, $5 million of which was paid following the public announcement of the execution of the merger agreement, $5 million of which is payable upon PSEG shareholder approval of the merger agreement and $10 million of which is payable upon completion of the merger.

Both Exelon and PSEG Shareholder Approvals Will Be Required to Complete the Merger (see page [    •    ])

For Exelon Shareholders:

        Approval of the proposal to issue shares of Exelon common stock as contemplated by the merger agreement requires the affirmative vote of at least a majority of the votes cast by holders of shares of Exelon common stock present in person or by proxy and entitled to vote on the issuance of shares of Exelon common stock as contemplated by the merger agreement as long as a quorum, which is the presence of holders of shares of Exelon common stock outstanding and entitled to cast at least a majority of the votes that all shareholders are entitled to cast on the matter, is present in person or by proxy and the total votes cast on the proposal represents at least a majority of the shares of Exelon common stock entitled to vote. Approval of the proposal to issue shares of Exelon common stock as contemplated by the merger agreement is a condition to completion of the merger.

        Because the holders of Exelon common stock immediately prior to completion of the merger will own a majority of the shares of Exelon common stock outstanding immediately following completion of the merger, a separate vote by the holders of Exelon common stock on the merger agreement or the merger itself is not required under Pennsylvania law.

        On [    •    ], 2005, which is the record date for determining those Exelon shareholders who are entitled to vote at the Exelon annual meeting, directors and executive officers of Exelon and their affiliates beneficially owned and had the right to vote [    •    ] shares of Exelon common stock, representing approximately [    •    ]% of the shares of Exelon common stock outstanding on the record date. To Exelon's knowledge, directors and executive officers of Exelon and their affiliates intend to vote their shares of common stock in favor of the proposal to issue shares of Exelon common stock as contemplated by the merger agreement.

For PSEG Shareholders:

        Approval of the merger agreement requires the affirmative vote of at least a majority of the votes cast by holders of shares of PSEG common stock present in person or by proxy and entitled to vote on

9

the approval of the merger agreement as long as a quorum, which is a majority of the shares of PSEG common stock outstanding, is present in person or by proxy.

        On [    •    ], 2005, which is the record date for determining those PSEG shareholders who are entitled to vote at the PSEG annual meeting, directors and executive officers of PSEG and their affiliates beneficially owned and had the right to vote [    •    ] shares of PSEG common stock, or approximately [    •    ]% of the outstanding shares of PSEG common stock outstanding on the record date. To PSEG's knowledge, directors and executive officers of PSEG and their affiliates intend to vote their shares of common stock in favor of the approval of the merger agreement.

Recommendations of Exelon and PSEG to Shareholders (see pages [    •    ] and [    •    ])

To Exelon Shareholders:

        The Exelon board of directors has reviewed and considered the terms of the merger and the merger agreement and has unanimously determined that the merger, including the issuance of shares of Exelon common stock as contemplated by the merger agreement, is advisable, fair to and in the best interests of Exelon and its shareholders and unanimously recommends that Exelon shareholders vote FOR the proposal to approve the issuance of shares of Exelon common stock as contemplated by the merger agreement.

To PSEG Shareholders:

        The PSEG board of directors has reviewed and considered the terms of the merger and the merger agreement and has unanimously determined that the merger is advisable, fair to and in the best interests of PSEG and its shareholders and unanimously recommends that PSEG shareholders vote FOR the proposal to approve the merger agreement and thereby approve the merger.

Completion of the Merger is Subject to Regulatory Clearance (see page [    •    ])

        To complete the merger, we must receive approval from and/or make filings with various federal and state regulatory agencies. At the federal level, these approvals include the approval of the Securities and Exchange Commission under PUHCA, the Federal Energy Regulatory Commission under the Federal Power Act and the Nuclear Regulatory Commission under the Atomic Energy Act. In addition, under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, the merger cannot be completed until we have made required notifications and given certain information and materials to the Antitrust Division of the United States Department of Justice and until specified waiting period requirements have expired. At the state level, among other required approvals, the New Jersey Board of Public Utilities and the Pennsylvania Public Utility Commission must approve or review the merger and the New York Public Service Commission must approve the indirect transfer of the ownership interest of a subsidiary of PSEG Power that has generation assets located in the State of New York. The Illinois Commerce Commission will review the merger but its approval is not required to complete the merger.

Exelon's Amended and Restated By-Laws will be Amended and Restated Following Completion of the Merger to, Among Other Things, Provide for Certain Governance Arrangements During a Transition Period Beginning Upon Completion of the Merger and Ending Three Years Following Completion of the Merger.

        Exelon has agreed to amend and restate its Amended and Restated By-laws to, among other things, provide for certain arrangements relating to its board of directors and management during a

10

transition period beginning upon completion of the merger and ending three years following completion of the merger, including the following:

•

upon completion of the merger, the Exelon board of directors will consist of 18 members, 12 of whom will be continuing Exelon directors and six of whom will be former PSEG directors;



•

with respect to the first and second elections of directors during the transition period, the Exelon board of directors is required, subject to its fiduciary duties and applicable laws and regulations, to nominate for election the legacy PSEG directors (or their successors) whose class is standing for election and the legacy Exelon directors (or their successors) whose class is standing for election;



•

during the transition period, the Exelon board of directors will, subject to its fiduciary duties and applicable laws and regulations, take any action necessary to ensure that any vacancy of a position on the Exelon board of directors previously held by a legacy PSEG director will be filled by a person nominated by the Exelon board of directors and approved by a majority of the legacy PSEG directors remaining on the Exelon board of directors, and that any vacancy of a position on the Exelon board of directors previously held by a legacy Exelon director will be filled by a person nominated by the Exelon board of directors and approved by a majority of the legacy Exelon directors remaining on the Exelon board of directors;



•

upon completion of the merger Mr. E. James Ferland, the current Chairman, President and Chief Executive Officer of PSEG, will become the non-executive Chairman of the Exelon board of directors;



•

Mr. Ferland will serve as non-executive Chairman of the Exelon board of directors until the earlier of (1) March 31, 2007, his announced date of retirement, and (2) the date on which Mr. Ferland no longer serves as a director of Exelon;



•

as non-executive Chairman of the Exelon board of directors, Mr. Ferland will preside at all meetings of the Exelon board of directors and will, in consultation with the Chief Executive Officer of Exelon, establish the agenda for board meetings and will have such other duties as may from time to time be requested by the Chief Executive Officer of Exelon;



•

when Mr. Ferland ceases to serve as the non-executive Chairman of the Exelon board of directors, the Chief Executive Officer of Exelon will be appointed as Chairman of the Exelon board of directors and continue in such role for the duration of the transition period and thereafter as determined by the Exelon board of directors; and



•

for at least the transition period, Mr. John W. Rowe, the current Chairman, President and Chief Executive Officer of Exelon, will continue to serve as the President and Chief Executive Officer of Exelon in charge of general supervision over the business and operations of Exelon.

        A copy of the form of Amended and Restated By-laws of Exelon is attached as Annex F to this joint proxy statement/prospectus and is incorporated by reference into this joint proxy statement/prospectus.

PSEG Executive Officers and Directors Have Interests in the Merger that May Be Different from, or in Addition to, the Interests of the PSEG shareholders (see page [    •    ])

        When PSEG shareholders consider their board of directors' recommendation that they vote in favor of the approval of the merger agreement, PSEG shareholders should be aware that PSEG executive officers and directors may have interests in the merger that are different from, or in addition to, PSEG shareholders' interests. Those interests include:

•

Exelon's agreement to appoint six PSEG directors to the Exelon board of directors following the merger and to amend and restate its Amended and Restated By-laws to provide that, during the

11

transition period, the Exelon board of directors will, subject to its fiduciary duties and applicable laws and regulations, nominate such former PSEG directors for election so that six of the 18 directors are former PSEG directors (or other persons approved by a majority of such former PSEG directors);

•

Exelon's agreement to appoint Mr. Ferland as the non-executive Chairman of the Exelon board of directors;



•

the assumption by Exelon of the PSEG stock options granted to PSEG executive officers and of PSEG equity-based awards granted to PSEG executive officers and directors outstanding at the time of completion of the merger;



•

the accelerated vesting of restricted shares held by each director of PSEG if, following completion of the merger, he or she ceases to serve as a director;



•

the accelerated vesting of specified PSEG stock options and other equity-based awards pursuant to employment agreements with the executive officers of PSEG and pursuant to the terms of PSEG's long-term incentive plans;



•

the entitlement of executive officers of PSEG to receive severance benefits following completion of the merger if they are terminated without cause or if they voluntarily terminate their employment for specified reasons as described under "The Merger—Interests of PSEG's Directors and Executive Officers in the Merger" beginning on page [    •    ] of this joint proxy statement/prospectus;



•

the permitted extension of the employment agreements between PSEG and specified executive officers of PSEG for two years following completion of the merger;



•

Exelon's agreement to provide officers and directors of PSEG with continuing indemnification rights; and



•

Exelon's agreement to provide directors' and officers' insurance for at least six years following the merger.

        As a result, the directors and officers of PSEG may be more likely to recommend the approval of the merger agreement than if they did not have these interests.

Completion of the Merger is Subject to the Satisfaction or Waiver of a Number of Conditions (see page [    •    ])

        Completion of the merger depends upon the satisfaction or waiver of a number of conditions, including the following:

•

approval of the merger agreement by the PSEG shareholders and approval by the Exelon shareholders of the issuance of shares of Exelon common stock as contemplated by the merger agreement;



•

authorization for listing by the New York Stock Exchange of the shares of Exelon common stock issuable pursuant to the merger agreement, subject to official notice of issuance;



•

expiration or termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended;



•

receipt of "final orders" for the "required statutory approvals" and the absence from such orders of any "burdensome order," which term includes, among other things, any order requiring either party to divest any nuclear assets (see "The Merger Agreement—Covenants" beginning on page [    •    ] of this joint proxy statement/prospectus for a discussion of these terms);

12

•

receipt of all other required government and regulatory consents, registrations, approvals and permits and authorizations, except for those the failure of which to obtain would not, individually or in the aggregate, reasonably be expected to have a material adverse effect on PSEG or on Exelon (assuming the merger had taken place);



•

receipt of all required consents or approvals from third parties, except for those the failure of which to obtain would not, individually or in the aggregate, reasonably be expected to have a material adverse effect on PSEG or on Exelon (assuming the merger had taken place);



•

absence of any law, judgment, injunction or other order by a governmental authority prohibiting completion of the merger;



•

compliance in all material respects by the parties with their respective obligations under the merger agreement;



•

absence of material breaches of the representations and warranties in the merger agreement;



•

receipt of opinions of counsel to Exelon and PSEG to the effect that the merger constitutes a "reorganization" within the meaning of Section 368(a) of the Internal Revenue Code; and



•

absence of a material adverse effect having occurred to the other party since the date of the merger agreement.

How the Merger Agreement May Be Terminated by Exelon and PSEG (see page [    •    ])

        Exelon and PSEG may mutually agree to terminate the merger agreement and abandon the merger at any time prior to completion of the merger, whether before or after the PSEG shareholders have approved the merger agreement and the Exelon shareholders have approved the issuance of shares of Exelon common stock as contemplated by the merger agreement.

        In addition, either party could decide, without the consent of the other, to terminate the merger agreement in a number of situations, including:

•

if the merger is not completed by June 20, 2006 (which date may be extended by six months by either party if all conditions to closing have been satisfied other than the receipt of approval by the FERC under Section 203 of the Federal Power Act, by the SEC under PUHCA or by any of the New Jersey, New York or Pennsylvania public utility commissions if Exelon and PSEG are reasonably satisfied such state commission is waiting for such FERC or SEC approval to be obtained prior to ruling and such ruling is required for completion of the merger);



•

if the required approval of the Exelon or PSEG shareholders is not obtained at the respective shareholder meetings;



•

if a nonappealable order has been entered prohibiting the merger or, in connection with the required statutory approvals, an order has been entered that is a burdensome order that is a nonappealable final order;



•

if the board of directors of the other party withdraws, qualifies or modifies its declaration, approval or recommendation in a manner adverse to the other party; or



•

if the other party breaches its representations, warranties or covenants in the merger agreement, which breach results in a failure of one of the conditions to completion of the merger being satisfied and is not curable or cured.

        The merger agreement may be terminated by PSEG prior to completion of the merger if, prior to the PSEG annual meeting:

•

the PSEG board of directors authorizes PSEG, subject to complying with the terms of the merger agreement, to enter into a definitive agreement with a third party concerning a

13

transaction that constitutes a "superior proposal" (see "The Merger Agreement—Covenants—No Solicitation" beginning on page [    •    ] of this joint proxy statement/prospectus for a discussion of this term) and PSEG notifies Exelon in writing that it intends to enter into the agreement;

•

Exelon does not make, within five business days of receipt of PSEG's written notification of its intention to enter into a definitive agreement for a superior proposal, an offer that the PSEG board of directors determines, in its reasonable good faith judgment after consultation with its financial advisors, is at least as favorable, from a financial point of view, to the shareholders of PSEG; and



•

prior to or concurrently with the termination of the merger agreement, PSEG pays to Exelon a termination fee of $400 million and Exelon's out-of-pocket expenses up to a maximum of $40 million.

        The merger agreement may also be terminated by PSEG prior to the PSEG annual meeting if Exelon enters into a definitive agreement with respect to a "parent acquisition transaction" (see "The Merger Agreement—Termination of Merger Agreement" beginning on page [    •    ] of this joint proxy statement/prospectus for a discussion of this term) or consummates such a transaction and PSEG notifies Exelon in writing that it is terminating the merger agreement within 10 business days of the earlier to occur of such parent acquisition transaction and the public announcement of the entry into such definitive agreement. If the merger agreement is terminated under this provision, Exelon will be required to pay PSEG a termination fee of $400 million and up to $40 million of PSEG's out-of-pocket expenses.

        The merger agreement may be terminated by Exelon prior to completion of the merger if:

•

PSEG's board of directors or a committee thereof recommends to PSEG shareholders a takeover proposal other than the merger;



•

a tender offer or exchange offer for 20% or more of the outstanding shares of PSEG capital stock is commenced and PSEG's board of directors fails to recommend against acceptance of such offer within 10 business days after such commencement;



•

PSEG breaches in any material respect its obligations under the no-solicitation provisions of the merger agreement; or



•

prior to Exelon's annual meeting, Exelon enters into a definitive agreement with respect to a parent acquisition transaction or consummates such a transaction and notifies PSEG in writing that it is terminating the merger agreement within 10 business days from the earlier to occur of such parent acquisition transaction and the public announcement of the entry into such definitive agreement.

Termination Fees and Expenses May Be Payable Under Some Circumstances (see page [    •    ])

        Generally, if the merger agreement is terminated by Exelon in specified circumstances where the PSEG board of directors has withdrawn, qualified or modified its declaration with respect to or its approval or recommendation of the merger agreement and the merger with Exelon in a manner adverse to Exelon, by either party in specified circumstances involving the acquisition of PSEG by another person, or by Exelon upon a material breach by PSEG of the no-solicitation provisions of the merger agreement, PSEG will be required to pay Exelon a termination fee of $400 million and up to $40 million of Exelon's out-of-pocket expenses.

        Generally, if the merger agreement is terminated by PSEG where the Exelon board of directors has withdrawn, qualified or modified its declaration with respect to or its approval or recommendation of the merger agreement, the issuance of shares of Exelon common stock as contemplated by the merger agreement and the merger in a manner adverse to PSEG, Exelon will be required to pay up to

14

$40 million of PSEG's out-of-pocket expenses. If the merger agreement is terminated by PSEG or Exelon where Exelon enters into a definitive agreement with respect to a parent acquisition transaction or consummates such a transaction, Exelon will be required to pay PSEG a termination fee of $400 million and up to $40 million of PSEG's out-of-pocket expenses.

Neither Exelon nor PSEG Shareholders Will Have Appraisal Rights in Connection with the Merger (see page [    •    ])

        Neither Exelon nor PSEG shareholders are entitled to dissenters' appraisal rights in connection with the merger.

Exelon Common Stock Will Be Listed on the New York Stock Exchange (see page [    •    ])

        The shares of Exelon common stock to be issued pursuant to the merger will be listed on the New York Stock Exchange. In addition, Exelon currently intends to list the shares of Exelon common stock issued in the merger on the Chicago Stock Exchange and the Philadelphia Stock Exchange.

Accounting Treatment of the Merger (see page [    •    ])

        Exelon will account for the merger under the purchase method of accounting for business combinations under accounting principles generally accepted in the United States.

PSEG Shareholders Will Hold Approximately [    •    ]% of the Outstanding Shares of Exelon Common Stock Following Completion of the Merger (see page [    •    ])

        Upon completion of the merger, Exelon will issue up to approximately [    •    ] million shares of Exelon common stock to PSEG shareholders as contemplated by the merger agreement. In addition, approximately [    •    ] million shares of Exelon common stock will be issuable pursuant to PSEG stock options and PSEG equity-based awards to be assumed by Exelon, approximately [    •    ] million of which will vest upon completion of the merger. Immediately following completion of the merger, it is expected that there will be approximately [    •    ] million shares of Exelon common stock issued and outstanding on a fully diluted basis. The shares of Exelon common stock to be issued to PSEG shareholders will represent approximately [    •    ] of the outstanding Exelon common stock after the merger on a fully diluted basis. This information is based on the number of Exelon and PSEG shares and PSEG equity-based awards and securities convertible into shares of PSEG common stock (PSEG's Participating Units) outstanding on [    •    ], 2005.

Due to Variances Between the State Business Corporation Law of Pennsylvania and New Jersey and between the Charters and Other Corporate Documents of Exelon and PSEG, Differences Exist Between the Rights of Exelon Shareholders and PSEG Shareholders (see page [    •    ])

        The rights of Exelon and PSEG shareholders under the business corporation law of Pennsylvania and New Jersey, respectively, are different. There are additional differences in the rights of Exelon shareholders and PSEG shareholders as a result of the provisions of the charters, by-laws and other corporate documents of each company. See "Comparison of Exelon/PSEG Shareholder Rights" beginning on page [    •    ] of this joint proxy statement/prospectus.

The Merger and the Performance of the Combined Company are Subject to a Number of Risks (see page [    •    ])

        There are a number of risks relating to the merger and to the businesses of Exelon, PSEG and the combined company following the merger. See "Risk Factors" beginning on page [    •    ] of this joint proxy statement/prospectus for a discussion of these and other risks and see also the documents that we have filed with the SEC and which we have incorporated by reference into this joint proxy statement/prospectus.

15

  Selected Historical Financial Information

        The following selected historical financial information is being provided to assist you in your analysis of the financial aspects of the merger. The Exelon annual historical information is derived from the audited consolidated financial statements of Exelon as of and for each of the years in the five-year period ended December 31, 2003. The PSEG annual historical information is derived from the audited consolidated financial statements of PSEG as of and for each of the years in the five-year period ended December 31, 2003. The data as of and for the nine months ended September 30, 2004 and 2003 has been derived from unaudited interim financial statements of both Exelon and PSEG and, in the opinion of each company's management, include all normal and recurring adjustments that are considered necessary for the fair presentation of the results for the interim period. The information is only a summary and should be read in conjunction with each company's historical consolidated financial statements and related notes contained in the Exelon and PSEG annual reports on Form 10-K for the year ended December 31, 2003 and quarterly reports on Form 10-Q for the periods ended March 31, 2004, June 30, 2004 and September 30, 2004, which have been incorporated by reference into this joint proxy statement/prospectus, as well as other information that has been filed with the SEC. See "Where You Can Find More Information" beginning on page [    •    ] of this joint proxy statement/prospectus for information on where you can obtain copies of this information. The historical results included below and elsewhere in this joint proxy statement/prospectus are not necessarily indicative of the future performance of Exelon, PSEG or the combined company.

16

  Exelon Selected Historical Financial Information

(1)

Reflects the effects of the merger of Exelon, Unicom Corporation and PECO on October 20, 2000 (the "Unicom Merger"). The Unicom Merger was accounted for using the purchase method of accounting with PECO as the acquiring company. Accordingly, financial results for 2000 consist of PECO's results for 2000 and Unicom results after October 20, 2000.

(2)

2003 results include a pre-tax charge of $945 million ($573 million after-tax) related to the impairment of Exelon's investment in Boston Generating, LLC and a pre-tax charge of $255 million ($166 million after-tax) related to the impairment of Exelon's investment in Sithe Holdings, Inc.

(3)

Upon adoption of Financial Accounting Standards Board Interpretation ("FIN") No. 46 (revised December 2003), "Consolidation of Variable Interest Entities" ("FIN No. 46-R") in 2003, the mandatory redeemable preferred securities of ComEd and PECO were reclassified as long-term debt to financing trusts as of December 31, 2003.

(4)

Per share information for 1999 through 2003 has been adjusted to reflect the 2-for-1 stock split that was distributed to Exelon shareholders on May 5, 2004.

17

  PSEG Selected Historical Financial Information

(1)

2002 results include after-tax charges of $368 million, or $1.76 per share, related to losses from PSEG Energy Holdings' Argentine investments. 1999 results include a charge of $804 million from a net writedown of PSEG's generation assets related to the completion of the State of New Jersey's electric restructuring initiative.

(2)

Includes capital lease obligations. The increase in Long-term obligations is related to the $2.5 billion securitization transaction in 2001.

(3)

This amount includes debt obligations between PSEG and PSE&G and their respective capital trusts due to the implementation of FIN No. 46-R which required the deconsolidation of such trusts. This implementation resulted in the removal of the preferred securities issued by the trusts from the PSEG consolidated financial statements and the addition of long-term debt between PSEG and PSE&G and their respective trusts equal to the amount of preferred securities issued by the trusts and the common equity investment contributed to the trusts.

18

  Selected Unaudited Pro Forma Condensed Combined Consolidated Financial Information

        The merger will be accounted for under the purchase method of accounting, which means the assets and liabilities of PSEG will be recorded, as of completion of the merger, at their respective fair values and added to those of Exelon. For a more detailed description of purchase accounting, see "The Merger—Accounting Treatment" beginning on page [    •    ] of this joint proxy statement/prospectus.

        We have presented below selected unaudited pro forma condensed combined consolidated financial information that reflects the purchase method of accounting and gives effect to the merger, in the case of the statement of operations information, as though the merger had occurred as of January 1, 2003 and, in the case of the balance sheet information, as though the merger had occurred as of September 30, 2004.

        The unaudited pro forma condensed combined consolidated financial information has been prepared giving effect to the issuance of 1.225 shares of Exelon common stock in exchange for each share of PSEG common stock.

        The unaudited pro forma condensed combined consolidated financial information may have been different had the companies actually been combined as of January 1, 2003. The selected unaudited pro forma condensed combined consolidated financial information does not reflect the effect of asset dispositions, if any, or cost savings that may result from the merger. You should not rely on the selected unaudited pro forma condensed combined consolidated financial information as being indicative of the historical results that would have occurred had the companies been combined or the future results that may be achieved after completion of the merger. The following selected unaudited pro forma condensed combined consolidated financial information has been derived from, and should be read in conjunction with, the Unaudited Pro Forma Condensed Combined Consolidated Financial Statements and related notes beginning on page [    •    ] of this joint proxy statement/prospectus.

(1)

Per share information for 2003 has been adjusted to reflect the 2-for-1 stock split that was distributed to Exelon shareholders on May 5, 2004.

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  Comparative Historical and Unaudited Pro Forma Per Share Information

        The following table sets forth selected historical per share information of Exelon and PSEG and unaudited pro forma condensed combined consolidated per share information reflecting the merger between Exelon and PSEG, under the purchase method of accounting, and the issuance of 1.225 shares of Exelon common stock in exchange for each share of PSEG common stock. You should read this information in conjunction with the selected historical financial information, included elsewhere in this joint proxy statement/prospectus, and the historical financial statements of Exelon and PSEG and related notes contained in the Exelon and PSEG annual reports on Form 10-K for the year ended December 31, 2003 and quarterly reports on Form 10-Q for the periods ended March 31, 2004, June 30, 2004 and September 30, 2004, which have been incorporated by reference into this joint proxy statement/prospectus. The unaudited Exelon pro forma condensed combined consolidated per share information is derived from, and should be read in conjunction with, the unaudited pro forma condensed combined consolidated financial statements and related notes beginning on page [    •    ] of this joint proxy statement/prospectus. The historical per share information is derived from audited financial statements of Exelon and PSEG as of and for the year ended December 31, 2003 and unaudited financial statements for the nine months ended September 30, 2004. The unaudited pro forma PSEG per share equivalents are calculated by multiplying the unaudited Exelon pro forma combined per share amounts by the exchange ratio of 1.225.

        The unaudited pro forma condensed combined consolidated per share information does not purport to represent what the actual results of operations of Exelon and PSEG would have been had the companies been combined during the periods presented or to project Exelon's and PSEG's results of operations that may be achieved after completion of the merger.

(1)

Per share information for 2003 has been adjusted to reflect the 2-for-1 stock split that was distributed to Exelon shareholders on May 5, 2004.

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Comparative Per Share Market Price and Dividend Information

        Exelon common stock and PSEG common stock are each listed on the New York Stock Exchange. Exelon's and PSEG's trading symbols are "EXC" and "PEG," respectively. The following table shows, for the calendar quarters indicated, based on published financial sources: (1) the high and low sale prices of shares of Exelon and PSEG common stock as reported on the New York Stock Exchange Composite Transaction Tape and (2) the cash dividends paid per share of Exelon and PSEG common stock. The sales prices and dividends with respect to Exelon common stock noted below have been retroactively restated for all periods to reflect the 2 for 1 stock split that was distributed to the Exelon shareholders on May 5, 2004.

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RISK FACTORS

        Exelon and PSEG will operate as a combined company in a market environment that involves significant risks, many of which will be beyond the combined company's control. In addition to the other information contained in or incorporated by reference into this joint proxy statement/prospectus, you should carefully consider the risks described below before deciding how to vote your shares. Additional risks and uncertainties not presently known to Exelon and PSEG or that are not currently believed to be important to you, if they materialize, also may adversely affect the merger and Exelon and PSEG as a combined company.

Risks Relating to the Merger

The value of Exelon shares to be received by PSEG shareholders will fluctuate.

        Upon completion of the merger, each share of PSEG common stock will be converted into the right to receive 1.225 shares of Exelon common stock. The number of shares of Exelon common stock to be issued pursuant to the merger for each share of PSEG common stock is fixed. The market price of Exelon common stock when the merger is completed may differ significantly from its market price at the date of this joint proxy statement/prospectus and at the date of the annual meetings of Exelon and PSEG. For example, during the 12-month period ended on [    •    ], 2005, the most recent practicable date prior to the mailing of this joint proxy statement/prospectus, Exelon common stock traded in a range from a low of $[    •    ] to a high of $[    •    ] and ended that period at $[    •    ]. See "Summary—Comparative Per Share Market Price and Dividend Information" beginning on page [    •    ] of this joint proxy statement/prospectus for more detailed share price information.

        Because of the number of regulatory approvals necessary to complete the merger, there may be a significant period of time (potentially up to [    •    ] months) between the date of the Exelon and PSEG annual meetings and the date on which the merger is completed. At the time of their respective annual meetings, Exelon and PSEG shareholders will not know the exact market value of the Exelon common stock that will be issued in connection with the merger. The value of the merger consideration to be received by PSEG shareholders will fluctuate with changes in the price of Exelon's common stock. Shareholders of Exelon and PSEG are urged to obtain current market quotations for Exelon and PSEG common stock.

The anticipated benefits of combining PSEG and Exelon may not be realized.

        Exelon and PSEG entered into the merger agreement with the expectation that the merger would result in various benefits, including, among other things, synergies, cost savings and operating efficiencies. Although we expect to achieve the anticipated benefits of the merger, achieving them, including the cost synergies, is subject to a number of uncertainties, including:

•

whether the businesses of Exelon and PSEG are integrated in an efficient and effective manner, including the successful completion of the corporate restructuring described under "The Merger—Corporate Restructuring";



•

whether the regulatory authorities whose approval is required to complete the merger impose conditions on the merger that may have a material adverse effect on the combined company;



•

the extent to which the state regulatory authorities whose approval is required to complete the merger require the combined company to share some of the expected synergies of the merger with customers; and



•

general competitive factors in the market place.

        Although the companies' plans for integration and operation of the combined company and its subsidiaries and divisions are focused on minimizing uncertainties in order to achieve these anticipated

22

benefits, no assurance can be given that these benefits will be achieved. Failure to achieve these anticipated benefits could result in increased costs, decreases in the amount of expected revenues and diversion of management's time and energy and could have an adverse effect on the combined company's business, financial condition, operating results and prospects.

Exelon and PSEG may be unable to successfully integrate their operations.

        The merger involves the integration of two companies that previously operated independently. The difficulties of combining each company's operations include:

•

the necessity of coordinating geographically separated organizations, systems and facilities; and



•

integrating personnel with diverse business backgrounds.

In addition, the integration of some of Exelon's and PSEG's operations will require regulatory approval.

        Exelon and PSEG recognize that the process of integrating operations could cause an interruption of, or loss of momentum in, the activities of one or more of the combined company's businesses, and we intend to address these issues. The diversion of management's attention and any delays or difficulties encountered in connection with the merger and the integration of the two companies' operations could have an adverse effect on the business, financial condition, operating results and prospects of the combined company after the merger, and could impair the combined company's ability to realize the anticipated benefits of the merger.

The application of the purchase method of accounting will result in approximately $7.9 billion of additional goodwill which could become impaired and adversely affect the market value of the combined company's common stock following completion of the merger.

        Under the purchase method of accounting, the total purchase price paid by Exelon in the merger will be allocated to PSEG's tangible assets and liabilities and identifiable intangible assets, if any are identified, based on their fair values as of the date of completion of the merger. The excess of the purchase price over those fair values will be recorded as goodwill. We expect that the merger will result in the creation of approximately $7.9 billion in goodwill based upon the application of purchase accounting. As a result, upon completion of the merger, the combined company will have approximately $13.1 billion in goodwill. To the extent the value of goodwill or intangibles becomes impaired, the combined company may be required to incur material charges relating to such impairment. Such a potential impairment charge could have a material impact on the combined company's operating results.

The combined company may be unable to obtain permission from the NJBPU to recover PSE&G's pension and other post-retirement benefit expenses, which could have an adverse effect on its cash flow and results of operation.

        PSE&G is permitted by its current NJBPU rate order to recover through its rates the amortized portion of its pension expenses and other post-retirement benefit expenses associated with its pension and post-retirement obligations. As a result of the application of the purchase method of accounting to these costs, the recognition of certain unrecognized pension and OPEB expenses will be accelerated and, as a result, will no longer be reflected in the calculation of pension expenses that PSE&G's current rate order permits it to recover. PSE&G estimates that it could have as much as $1.1 billion in unrecognized pension and OPEB expenses that PSE&G may be unable to recover following completion of the merger unless it obtains approval from the NJBPU to permit continued recovery of those expenses in the manner the current rate order permits. Exelon and PSEG have made it a condition to completion of the merger that PSE&G receive an order from the NJBPU permitting PSE&G to

23

continue to recover the pension expenses as it did prior to completion of the merger. The NJBPU has issued similar orders in other merger proceedings and such an order would not be expected to increase rates above current levels; however, Exelon and PSEG cannot assure you that PSE&G will receive such an order from the NJBPU or that if it does receive such an order, it will be permitted in future rate proceedings to continue to recover these expenses. Failure to obtain or maintain the right to recover the pension and OPEB expenses would have an adverse effect on the combined company's cash flow and results of operations.

Exelon and PSEG will incur significant transaction and merger-related integration costs in connection with the merger.

        Exelon and PSEG expect to incur costs associated with consummating the merger and integrating the operations of the two companies, as well as approximately $41 million in transaction fees in the case of Exelon and $29 million in the case of PSEG. The estimated $41 million of transaction costs incurred by Exelon will be included as a component of the purchase price for purposes of purchase accounting. The amount of transaction fees expected to be incurred is a preliminary estimate and subject to change. Exelon currently estimates integration costs associated with the merger to be approximately $700 million over a period of 4 years, with approximately $400 million being incurred in the first year after completion of the merger and approximately $150 million being incurred in the second year after completion of the merger. Exelon is in the early stages of assessing the magnitude of these costs and, therefore, these estimates may change, and additional unanticipated costs may be incurred in the integration of the businesses of Exelon and PSEG. Although Exelon and PSEG believe that the elimination of duplicative costs, as well as the realization of other efficiencies related to the integration of the businesses, will offset incremental transaction and merger-related costs over time, we cannot assure you that this net benefit will be achieved in the near term, or at all.

Exelon and PSEG will be subject to business uncertainties and contractual restrictions while the merger is pending which could adversely affect their businesses.

        Uncertainty about the effect of the merger on employees and customers may have an adverse effect on Exelon, PSEG and consequently on the combined company. Although Exelon and PSEG intend to take steps to reduce any adverse effects, these uncertainties may impair Exelon's and PSEG's ability to attract, retain and motivate key personnel until the merger is consummated and for a period of time thereafter, and could cause customers, suppliers and others that deal with Exelon and PSEG to seek to change existing business relationships with Exelon and PSEG. Employee retention may be particularly challenging during the pendency of the merger, as employees may experience uncertainty about their future roles with the combined company. If, despite Exelon's and PSEG's retention efforts, key employees depart because of issues relating to the uncertainty and difficulty of integration or a desire not to remain with the combined company, the combined company's business could be seriously harmed. In addition, the merger agreement restricts Exelon and PSEG from making certain acquisitions and taking other specified actions until the merger occurs or the merger agreement terminates. These restrictions may prevent Exelon and PSEG from pursuing otherwise attractive business opportunities and making other changes to their businesses that may arise prior to completion of the merger or termination of the merger agreement. Please see the section titled "The Merger Agreement—Covenants" beginning on page [    •    ] of this joint proxy statement/prospectus for a description of the restrictive covenants applicable to PSEG and Exelon.

The combined company may be subject to adverse regulatory conditions following completion of the merger.

        Before the merger may be completed, various approvals or consents must be obtained from FERC, the SEC, the NRC and various utility regulatory, antitrust and other authorities in the United States and in foreign jurisdictions. The governmental authorities from which these approvals are required may

24

impose conditions on completion of the merger or require changes to the terms of the merger. These conditions or changes could have the effect of delaying completion of the merger or imposing additional costs on or limiting the revenues of the combined company following the merger, any of which might have a material adverse effect on the combined company following completion of the merger.

        Exelon and PSEG have filed or will file applications for the required statutory approvals with the governmental authorities described above, including a market concentration mitigation plan with FERC. The market concentration mitigation plan included with the companies' filings with FERC contemplates (1) the divestiture of fossil fuel generating facilities with 2,900 MW of generating capacity and (2) the transfer of control of 2,600 MW of baseload nuclear capacity through either long-term firm baseload energy sales contracts or an annual auction. Exelon and PSEG have not offered to divest any nuclear generating facilities and do not anticipate doing so. FERC could, however, condition its approval of the merger on the parties agreeing to divest or transfer control of a greater amount of capacity and/or to divest additional generation assets. If that were to occur, it could have the effects described in the previous paragraph. See "The Merger—Regulatory Matters Relating to the Merger" beginning on page [    •    ] of this joint proxy statement/prospectus for a discussion of the required statutory approvals and the filings by Exelon and PSEG.

Some of the directors and executive officers of PSEG and Exelon have interests and arrangements that could have affected their decision to support or approve the merger.

        The interests of some of the directors and executive officers of PSEG in the merger are different from, and may be in addition to, those of PSEG shareholders generally and could have affected their decision to support or approve the merger. These interests include those described under "The Merger—Interests of PSEG's Directors and Executive Officers in the Merger" beginning on page [    •    ] of this joint proxy statement/prospectus. As a result, the directors and officers of PSEG may be more likely to recommend to PSEG's shareholders the approval of the merger agreement than if they did not have these interests.

        The interests of some of the executive officers of Exelon in the merger are different from, and may be in addition to, those of Exelon shareholders generally and could have affected their decision to support the merger. The Amended and Restated By-laws of Exelon to be adopted upon completion of the merger provide that for at least the three-year transition period following completion of the merger, Mr. Rowe will be the Chief Executive Officer of Exelon and that when Mr. Ferland ceases to serve as the non-executive Chairman of the Exelon board of directors, the Chief Executive Officer of Exelon will be appointed Chairman of the Exelon board of directors. In addition, the merger agreement permits Exelon to amend its severance agreements and plans to treat the merger as a change in control under those agreements and plans. The Exelon compensation committee has recently considered changes to the senior management severance plan that would provide certain benefits to participating executives whose employment terminates in connection with the merger, including the accelerated vesting of outstanding stock options and restricted stock awards. No such changes have been formally adopted to date, but it is currently anticipated that such changes will be adopted on or before the closing of the merger. As a result, the officers of Exelon may be more likely to recommend to Exelon's shareholders the approval of the issuance of shares of Exelon common stock as contemplated by the merger agreement.

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Risks Relating to the Business of the Combined Company

Under the combined company's holding company structure, the payment of dividends to shareholders will be subject to the ability of its subsidiaries to pay dividends.

        Exelon and PSEG are, and the combined company will be, a holding company with no material assets other than the stock of its subsidiaries. Accordingly, all of the combined company's operations will be conducted by its subsidiaries. The combined company's ability to pay dividends on its common stock will depend on the payment to it of dividends by its operating subsidiaries. These subsidiaries' payments of dividends to the combined company in turn depend on their results of operations and cash flows. ComEd is subject to a financing order which requires that it maintain a ratio of common equity to total capitalization of at least 30%. This order has the effect of generally restricting the payment of dividends to the amount of retained or current earnings and precludes any payment if the subsidiary's common equity is less than 30% of its capitalization. While PSE&G currently has no such restrictions, the NJBPU as a condition to approval of other utility mergers has imposed dividend restrictions. We can give no assurance that a similar restriction will not be imposed on PSE&G. In addition, PSEG Energy Holdings and its subsidiaries are parties to debt agreements that restrict their ability to pay dividends, make cash distributions or otherwise transfer funds to PSEG, or after completion of the merger, the combined company.

Fluctuations in the combined company's operating results may affect the market prices of its common stock.

        The market price of the combined company's common stock may fluctuate because its operating results may vary. Variations in the combined company's operating results can result from many factors, including factors beyond its control, such as weather and economic conditions. The combined company's results of operations may also vary significantly from quarter to quarter because of the timing of certain events and other factors, including the other risk factors set forth in this joint proxy statement/prospectus. Therefore, you should not rely on Exelon's, PSEG's or the combined company's results of operations during any particular quarter as an indication of the combined company's results for a full year or any other quarter.

Exelon's and PSEG's businesses are, and the combined company's business will be, subject to extensive regulation that will affect their operations and costs.

        Exelon and PSEG are, and the combined company will be, subject to regulation by the SEC under PUHCA, by FERC and the NRC, by federal, state and local authorities under environmental laws and by state public utility commissions under laws regulating Exelon's and PSEG's distribution businesses, among others. Regulation will affect almost every aspect of the combined company's businesses, from its fundamental business management actions to its ability to:

•

determine the terms and rates of its transmission and distribution businesses' services;



•

make acquisitions;



•

issue equity or debt securities;



•

engage in transactions between its utilities and other subsidiaries and affiliates; and



•

pay dividends.

        Changes in regulation can cause delays in or affect business planning and transactions and can increase the combined company's costs. As part of retail electric restructuring initiatives in Illinois and Pennsylvania and other regulatory proceedings, ComEd's and PECO's rates are currently subject to limitations, including:

•

a freeze on ComEd's bundled rates through 2006;

26

•

a limitation on ComEd's return on equity through 2006;



•

a cap on PECO's electric transmission and distribution rates through 2006;



•

a cap on PECO's generation rates through 2010; and



•

scheduled recovery of PECO's electric stranded costs that will increase amortization expenses through 2010.

        These rate provisions limit the ability of ComEd and PECO to recover cost increases or the costs of new investments. As a result, ComEd and PECO must effectively manage their costs to maintain their current profitability.

        In addition, the end of the transition periods in Illinois and Pennsylvania include uncertainties, including the source and pricing of generation services to be provided by PECO and methodology for wholesale supply procurement in Illinois and Pennsylvania and recovery of supply costs from retail customers. The end of the transition periods in Illinois and Pennsylvania also presents uncertainty for Exelon Generation, which sells a significant portion of its output to ComEd and PECO under long-term purchased power agreements. The agreement with ComEd, which expires at the end of 2006, may not be replaced with a similar arrangement. If the agreement is not replaced, Exelon Generation will need to sell more power at market-based prices, which may include an auction-based model, or enter into new contractual arrangements with third parties, which may have shorter durations and lower volume sales. Increased market sales and new contractual arrangements may adversely affect Exelon Generation's credit risk, due to an increase in the number of customers and the loss of a highly predictable revenue source, and may increase the variability of Exelon's earnings.

        PSE&G's New Jersey base rates for electric and gas distribution are subject to regulation by the NJBPU and are effective until a new base rate case is filed and concluded. In addition, limited categories of costs are recovered through adjustment charges that are periodically reset to reflect current costs. Inability to recover material costs not included in base rates or adjustment clauses could have an adverse effect on cash flow and financial position of the combined company.

        PSEG Global's electric and gas distribution facilities located in various foreign jurisdictions are rate-regulated enterprises. Governmental authorities establish rates charged to customers. While these rates are designed to cover all operating costs and provide a return, considerable fiscal and cash uncertainties in certain countries due to local regulation or economic, political and social crisis could have an adverse impact. In addition, future rates may not be adequate to provide cash flow to pay principal and interest on the debt of PSEG Global's subsidiaries' and affiliates or to enable its subsidiaries and affiliates to comply with the terms of debt agreements.

The combined company's financial performance will be affected by the amortization and eventual completion of stranded cost recovery for ComEd and PECO.

        ComEd's and PECO's current retail electric rates include charges to recover stranded costs that might not otherwise be recoverable in a fully competitive market. The amount of stranded cost recovery by ComEd varies annually depending on wholesale market prices and other factors, with stranded cost recovery ending at the end of 2006. Stranded cost recovery by PECO continues through 2010. Although the annual amount of stranded cost recovery is scheduled to increase during that period, annual increases in amortization of PECO's stranded cost recovery and the corresponding reductions in the return on the unamortized portion of stranded cost recovery will adversely affect PECO's results through 2010. Further, the termination of stranded cost recovery at the end of 2006 for ComEd and at the end of 2010 for PECO could significantly adversely affect their future results of operation.

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Providing reliable service to the combined company's customers is necessary to achieve desired operating results.

        The combined company's transmission and distribution businesses, referred to in this joint proxy statement/prospectus as the "energy delivery business," will be obligated to provide safe and reliable service to their customers. Meeting this commitment requires significant capital and other resources. Failure to provide safe and reliable service, including from equipment failures in electric and gas delivery systems, could adversely affect the combined company's operating results through reduced revenues and increased maintenance and capital costs. In addition, under Illinois law, ComEd can be required to pay damages to its customers in the event of extended outages affecting large numbers of its customers. The North American transmission grid is highly interconnected and, in extraordinary circumstances, disruptions at a point within the grid can cause a systemic response that results in an extensive power outage on the combined company's delivery systems. Power outages in ComEd's, PECO's or PSE&G's service territories could occur even if the disruptions originate outside of those territories.

The combined company's energy delivery business will be obligated as the provider-of-last-resort to provide energy to all retail customers in its service territories, which makes it difficult to predict and plan for load requirements.

        PECO, ComEd and PSE&G serve as the provider-of-last-resort, referred to in this proxy statement/prospectus as a "POLR," for energy for all retail customers in their respective electric and gas service territories in Illinois, Pennsylvania, and New Jersey. As POLR suppliers, PECO, ComEd and PSE&G could be required to secure load requirements sufficient to serve all customers in their respective service territories in the event that customers do not choose alternate suppliers or a third party supplier is unable to satisfy its obligations. As a result, planning has a higher level of uncertainty than that traditionally experienced due to weather and the economy, and it is more difficult to predict and plan for the number of customers and their associated energy demand.

The combined company's energy generation business will have contractual obligations to certain energy delivery businesses to provide full requirements service to satisfy POLR requirements, which makes it difficult to predict and plan for load requirements and may result in increased costs to the business.

        The combined companies' generation business will have contractual obligations to certain energy delivery businesses to supply requirements service to such companies to satisfy all or a portion of such companies' POLR obligations. The uncertainty regarding the amount of load that the combined company's generation business must prepare for will likely increase the cost of the combined company's generation business. A significant under-estimation of load requirements could result in the combined company's generation business not having enough power to cover its load obligation, in which case it would be required to buy power from third parties at prevailing market prices. Those prices may not be as favorable or as manageable as the long-term supply costs of the combined company's generation business and thus could increase its costs. The divestiture of generation assets or capacity in order to obtain the required regulatory approvals to complete the merger, increases the likelihood of the combined company's generation business not having enough power to cover its load obligation.

The revenues and cash flows of the combined company's energy delivery business will be affected by factors beyond the combined company's control.

        The revenues of the combined company's energy delivery business will be affected by the demand for electricity and natural gas. That demand can vary greatly based upon:

•

weather conditions, seasonality and temperature extremes;



•

availability of competitively priced alternative energy sources; and

28

•

fluctuations in economic activity and growth in the combined company's service territories.

        Weather conditions, accidents and other catastrophic events can disrupt or limit the ability of the combined company's energy delivery business to deliver electricity and natural gas to its customers. Very warm and very cold temperatures, especially for prolonged periods, can dramatically increase the demand for electricity and natural gas for cooling and heating. The pricing of alternative energy sources may affect the demand of customers, such as commercial and industrial customers, who have the ability to use alternative energy sources in their operations.

The combined company's generation business may incur substantial costs and liabilities due to its ownership and operation of nuclear generating facilities.

        The ownership and operation of nuclear generating facilities involve risks, including:

•

mechanical or structural problems;



•

inadequacy or lapses in maintenance protocols;



•

impairment of reactor operation and safety systems due to human error;



•

costs of storage, handling and disposal of nuclear materials, including the availability or unavailability of a permanent repository for spent nuclear fuel;



•

limitations on the amounts and types of insurance coverage commercially available;



•

uncertainties regarding both technological and financial aspects of decommissioning nuclear generating facilities; and



•

environmental regulatory risks associated with regulatory change.

        The material risks known or currently anticipated by Exelon and PSEG that could affect the ability of the combined company's nuclear generation business to achieve desired levels of profitability of Exelon and PSEG's generation businesses are:

        Capacity Factors.    The combined company's nuclear fleet must operate at consistently high capacity factors in order for it to produce efficient, low-cost energy and sustain the current profitability levels of Exelon and PSEG.

        Life Extensions.    Exelon Generation's nuclear generating facilities are currently operating under 40-year NRC licenses. Exelon Generation has received 20-year extensions for the operating licenses for Peach Bottom units 2 and 3, Dresden units 2 and 3 and Quad Cities nuclear generating facilities. In December 2004, the NRC issued an order that will permit Oyster Creek to operate beyond its license expiration in April 2009 if the NRC has not completed reviewing the application for extension. The application for Oyster Creek's license renewal is expected to be filed by August 2005 to comply with this agreement. Exelon Generation is currently evaluating other nuclear facilities for possible license extension. PSEG Power's nuclear generating facilities are currently operating under NRC licenses that expire in 2016, 2020 and 2026. The operating license extension process takes approximately four to five years from the commencement of the project until completion of NRC review. Exelon Generation and PSEG Power cannot be sure that they will receive the requested extensions or be able to operate the facilities for all or any portion of any extended license.

        Regulatory Risk.    The NRC may modify, suspend or revoke licenses, shut down a nuclear facility and impose civil penalties for failure to comply with the Atomic Energy Act, related regulations or the terms of the licenses for nuclear generating facilities. A change in the Atomic Energy Act or the applicable regulations or licenses may require a substantial increase in capital expenditures or may result in increased operating or decommissioning costs.

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        Operational Risk.    Operations at any of the combined company's nuclear generation plants could degrade to the point where the combined company has to shut down the plant or operate at less than full capacity. If this were to happen, identifying and correcting the causes may require significant time and expense. The combined company may choose to close a plant rather than incur the expense of restarting it or returning it to full capacity. In either event, the combined company may lose revenue and incur increased fuel and purchased power expense to meet its supply commitments.

        Nuclear Accident Risk.    Accidents and other unforeseen problems have occurred both in the United States and elsewhere. The consequences of an accident can be severe and include loss of life and property damage. Any resulting financial impact from a nuclear accident may exceed the combined company's resources, including insurance coverages.

        Nuclear fuel quality may affect costs.    The quality of nuclear fuel utilized by the combined company's generation business can affect the efficiency and costs of its operations. Certain Exelon Generation nuclear generating facilities have recently identified a limited number of fuel performance issues. Remediation actions have resulted in increased costs due to accelerated fuel amortization and/or increased outage costs and could continue to do so. It is difficult to predict the total cost of these remediation procedures.

        Nuclear Concentration.    Following completion of the merger, it is expected that, prior to giving effect to any divestitures required by governmental authorities to complete the merger, approximately 46% of the combined company's owned generation capacity will be nuclear and the combined company will own approximately 20% of the nuclear generation capacity in the United States. Accordingly, the combined company will have greater exposure to risks that adversely affect the nuclear generation industry compared to other companies in the utility industry.

The combined company's generation business may incur substantial costs and liabilities and be exposed to volatility as a result of its participation in the wholesale energy markets.

        Price Fluctuations.    Exelon Generation sells electricity in both the wholesale bilateral markets and spot markets. These sales expose it to the risks of rising and falling prices in those markets, and its cash flows may vary accordingly. To the extent it does not supply power to serve the needs of ComEd and PECO at fixed rates mandated by state regulatory commissions, its cash flows will largely be determined by wholesale prices of electricity and its ability to market successfully energy, capacity and ancillary services. At any given time, the wholesale spot-market price of electricity for each hour is generally determined by the cost of supplying the next unit of electricity to the market during that hour. In many cases, the next unit of electricity supplied would be supplied from generating stations fueled by fossil fuels, primarily coal and natural gas. Consequently, the open market wholesale price of electricity may reflect the cost of coal and natural gas plus the cost to convert the fuel to electricity, commonly known as the spark spread. Therefore, changes in the supply and cost of coal and natural gas may impact the open market wholesale price of electricity.

        PSEG Power expects to meet its supply obligations through a combination of generation and energy purchases managed by PSEG ER&T. PSEG Power also enters into trading positions related to its generation assets and supply obligations. To the extent PSEG Power does not hedge its costs, PSEG Power will be subject to the risk of price fluctuations that could affect its future results including variability in costs, such as changes in the expected price of energy and capacity that PSEG Power sells into the market, increases in the price of energy purchased to meet its supply obligations or the amount of excess energy sold into the market, the cost of fuel to generate electricity and the cost of emission credits and congestion credits that are used by PSEG Power to transmit electricity.

        Third Party Credit Risk.    In the bilateral markets, Exelon Generation and PSEG Power are exposed to the risk that counterparties that owe them money or energy as a result of market

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transactions will not perform their obligations. For example, energy supplied by third-party generators under long-term agreements represents a significant portion of Exelon Generation's overall capacity and may provide a significant portion of PSEG's NJBPU auction load requirements. These generators face operational risks, such as those that Exelon Generation and PSEG Power face, and their ability to perform depends on their financial condition. In the event the counterparties to these arrangements fail to perform, Exelon Generation and PSEG Power might be forced to honor the underlying commitment at then-current market prices and incur additional losses, to the extent of amounts, if any, already paid to the counterparties, and increased cost of energy or capacity to the extent the market price exceeds the contract price. In the spot markets, Exelon Generation and PSEG Power are exposed to the risks of whatever default mechanisms exist in that market, some of which attempt to spread the risk across all participants, which may not be an effective way of lessening the severity of the risk and the amounts at stake.

        Risk of Credit Downgrades.    Exelon Generation's and PSEG Power's trading businesses are, and the trading business of the combined company will be, required to meet credit quality standards. If either of Exelon Generation or PSEG Power, or the generation business of the combined company after the merger, were to lose its investment grade credit rating, it would be required under trading agreements to provide collateral in the form of letters of credit or cash, which may materially adversely affect the liquidity of Exelon or PSEG, or after completion of the merger, the combined company. If Exelon Generation had lost its investment grade credit rating as of December 31, 2004, it would have been required to provide approximately $600 million in collateral. If PSEG Power had lost its investment grade credit rating as of December 31, 2004, it would have been required to provide approximately $740 million in collateral.

        Immature Markets.    The wholesale spot markets are new and evolving markets that vary from region to region and are still developing practices and procedures. Exelon Generation and PSEG Power cannot predict what form any of these markets will eventually take or what roles they will play in them. Problems in or the failure of any of these markets, as was experienced in California in 2000, could adversely affect the combined company's generation business.

        Hedging.    The combined company's trading operation will buy and sell energy and other products in the wholesale markets and enter into financial contracts to manage risk and hedge various positions in the combined company's power generation profiles. This activity, along with the effects of any specialized accounting for the trading contracts, may cause volatility in the future results of operations of the combined company and affect the payment of dividends.

The combined company's generation business will rely upon FERC authority to continue to sell power at market-based rates. FERC continues to refine its policy with regard to its market-based rate authority.

        The combined company's generation business will rely upon market-based rate authority from FERC to sell its power in the marketplace. In 2004, FERC substantially revised its generation market power screen, which it uses to determine if power sellers should be entitled to sell at market-based rates. FERC is considering further changes to its generation market power screen. FERC's revised screen is an indicative, rather than decisive, tool, and includes two separate analyses: (a) an uncommitted pivotal supplier analysis and (b) a market share analysis that is to be prepared on a seasonal basis. The combined company's generation business will be subject to FERC's revised market power screens. If the combined company's generation business does not pass the screens, it will be required either to satisfactorily explain to FERC why the combined company should nonetheless be permitted to sell power at market-based rates or submit a mitigation plan. If such efforts were not successful, the combined company could lose its ability to sell at market-based rates, which loss could have a material adverse effect on the combined company's generation business. Any mitigation plan

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that might be required in order to retain market-based rate authority could also adversely affect the revenues of the combined company's generation business.

Impairment of ComEd's goodwill could adversely affect the combined company's results of operation and could restrict ComEd's ability to pay dividends to the combined company.

        At September 30, 2004, ComEd had recorded goodwill of $4.7 billion. This goodwill was recognized and recorded in connection with the merger of Unicom Corporation and PECO. Under generally accepted accounting principles, the goodwill will remain at its recorded amount unless it is determined to be impaired, based upon an annual (or more often as circumstances dictate) analysis of ComEd's expected future cash flows. If an impairment of goodwill is determined at ComEd, the amount of the impaired goodwill will be written off and expensed at ComEd. However, a goodwill impairment charge at ComEd may not affect the combined company's results of operations. The combined company's goodwill impairment test would include assessing the expected future cash flows of the entire energy delivery segment (a single reporting unit, which will include ComEd, PECO and PSE&G, as defined under current accounting guidance), not just ComEd's expected future cash flows. ComEd's cash flows include competitive transition charges, which will cease at the end of 2006, unless there is a legislative or regulatory change, and collections from traditional bundled customers at tariffed rates. ComEd's cash flows will be affected by other factors, including the restructuring of the power purchase agreement, referred to in this joint proxy statement/prospectus as a "PPA," with Exelon Generation. Absent another source of revenues to replace the loss of competitive transition charge revenue or changes in its cost structure, there is a reasonable possibility that goodwill will be impaired at ComEd, and possibly Exelon, in 2005 or later periods. Under current regulations, a significant goodwill impairment may restrict ComEd's ability to pay dividends to the combined company with the result that the combined company's dividends would depend upon the receipt of dividends from other subsidiaries. For a discussion of potential impairment charges in connection with accounting for the merger under the purchase method of accounting, see "—Risks Relating to the Merger—The application of the purchase method of accounting will result in approximately $7.9 billion of additional goodwill which could become impaired and adversely affect the market value of the combined company's common stock following completion of the merger" on page [    •    ] of this joint proxy statement/prospectus.

The price of the combined company's common stock may be affected by the general perception of the energy and utility sectors of the economy.

        Events, such as the August 14, 2003 blackout, those involving Enron Corporation, political unrest in oil-producing countries and the California energy crisis of 2000, in addition to the fact that the energy industry is changing and subject to greater risk, could adversely affect investors' perception of the energy and utility sectors and could adversely affect the equity prices of companies in those sectors. PSEG and Exelon cannot predict, and the combined company will not be able to predict, what news or events will affect the public or how any news or events affect the market price of the combined company's common stock, but fluctuations due to such news and events could be severe and any negative effects could be long lasting.

The Internal Revenue Service might successfully challenge certain leveraged lease transactions entered into by PSEG, which could have a material adverse impact on the combined company's operating results.

        In 1996 through 2002, PSEG through its subsidiary PSEG Resources, entered into a number of leveraged leasing transactions in the ordinary course of PSEG Resources' business. The IRS is likely to argue that certain of those transactions are of a type that it has announced its intention to challenge, and PSEG and Exelon understand that similar transactions entered into by other companies have been

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the subject of review and challenge by the IRS. As of September 30, 2004, the total gross investment by PSEG Resources in such transactions was approximately $1.4 billion.

        The IRS is presently reviewing the tax returns of PSEG and its subsidiaries for tax years 1997 through 2000, years when PSEG Resources entered into these transactions. The IRS is aware of these lease transactions and has requested information and documents associated with them. To date, the IRS has not proposed to disallow any deductions claimed relative to these transactions, but may propose such disallowances in the future. If the tax benefits associated with the lease transactions were successfully challenged by the IRS, PSEG or, following completion of the merger, the combined company would be assessed interest and possibly penalties in addition to any underpayments of tax. During the time period of 1997 through 2000, these transactions reduced current tax liabilities of PSEG by approximately $240 million and during the subsequent time period of 2001 though 2004, these and similar transactions reduced the current tax liabilities of PSEG by approximately $301 million. Interest that would be assessed on these potential deficiencies, if associated deductions were disallowed, would be approximately $100 million through December 31, 2004.

        It is presently unclear the extent to which the IRS will seek to disallow deductions associated with lease transactions, if at all, and, if it were to do so, the extent to which any such challenge would be successful. If deductions associated with these transactions entered into by PSEG were successfully challenged by the IRS, it could have a material adverse impact on the combined company's operating results and could impact future returns on these transactions.

        The Financial Accounting Standards Board, referred to in this joint proxy statement/prospectus as "FASB," is currently considering a modification to the Generally Accepted Accounting Principles, referred to in this joint proxy statement/prospectus as "GAAP," for leveraged leases. Under present GAAP, a tax settlement with the IRS that results merely in a change in the timing of tax liabilities would not require an accounting repricing of the lease investment. As such, income from the lease would continue to accrue at the original economic yield computed for the lease and there would be no writedown of the lease investment.

        A modification currently being considered by the FASB could require a lease to be repriced in the event a change in the timing of tax liabilities has a significant impact on the economic yield of the lease and to be retested to determine if it qualifies for leveraged lease accounting. If this or a similar modification were to be adopted by the FASB, a successful challenge by the IRS to the tax treatment of the leases referred to above (or a settlement with the IRS), could trigger a lease repricing. If a repricing were to occur, there could be a material adverse impact on the combined company's operating results. Further, such a successful challenge or settlement may cause the lease to fail to qualify for leveraged lease accounting. This would require that the non-recourse debt associated with the lease be brought onto the balance sheet of the combined company, which also could have a material adverse impact on the combined company's operating results. It is presently unclear what modifications, if any, will be adopted by the FASB, the timing of any such modification and the effect of any such modification on the operating results of PSEG or the combined company.

The IRS might successfully challenge certain tax positions taken by Exelon in connection with certain sale transactions, which could have a material adverse impact on the combined company's operating results.

        Exelon, through its ComEd subsidiary, has taken certain tax positions, which have been disclosed to the IRS, to defer the tax gain on a 1999 sale of its fossil generating assets. As of December 31, 2004, deferred tax liabilities related to the fossil plant sale are reflected in Exelon's consolidated balance sheets, with the majority allocated to the consolidated balance sheets of ComEd and the remainder to the consolidated balance sheets of Exelon Generation. The 1999 income tax liability deferred as a result of these transactions was approximately $1.1 billion. Exelon's ability to defer a portion of this liability depends on whether its characterization of a portion of the sales proceeds as having been

33

received in connection with an "involuntary conversion" is proper. Exelon's ability to defer the remainder of this liability may depend in part on whether its tax characterization of a lease transaction it entered into in connection with the sale is proper. The IRS might argue that the lease transaction is of a type it has announced its intention to challenge, and Exelon understands that somewhat similar transactions entered into by other companies have been the subject of review and challenge by the IRS. Changes in IRS interpretations of existing primary tax authority or challenges to Exelon's tax positions could have the impact of accelerating future income tax payments and increasing interest expense related to the deferred tax gain that becomes current. Any required payments could be significant to the cash flows of Exelon. Exelon's management believes Exelon's reserve for interest, which has been established in the event that such positions are not sustained, has been appropriately recorded in accordance with SFAS No. 5, "Accounting for Contingencies." However, the ultimate outcome of such matters could result in additional unfavorable adjustments to the results of operations, and such adjustments could be material. Federal tax returns covering the period of the 1999 sale are currently under IRS audit. Final resolution of this matter is not anticipated for several years.

        It is presently unclear the extent to which the IRS will seek to disallow the deferral of tax liability resulting from the 1999 sale of fossil generating assets, if at all, and if it were to do so, the extent to which any such challenge would be successful. If the deferral were successfully challenged by the IRS, it could have a material adverse impact on the combined company's operating results.

Because a portion of the combined company's business will be conducted outside the United States, adverse international developments could negatively impact its business.

        The combined company will have assets operating outside the United States. The economic and political conditions in certain countries where PSEG Global has interests present risks that may be different from, or more extensive than, those found in the United States including:

•

foreign currency fluctuations;



•

risks of war;



•

expropriation;



•

nationalization;



•

renegotiation or nullification of existing contracts; and



•

changes in law or tax policy.

        Changes in the legal environment in foreign countries in which PSEG Global has investments could make it more difficult to obtain non-recourse project refinancing on suitable terms and could impair PSEG Global's ability to enforce its rights under agreements relating to such projects. In addition, such changes could make it more difficult for the combined company to pursue an accelerated strategy of selling certain of PSEG Global's investments that no longer meet strategic objectives of the combined company.

        Operations in foreign countries also present risks associated with currency exchange and convertibility, inflation and repatriation of earnings. In countries in which PSEG Global operates in the future, economic and monetary conditions and other factors could affect PSEG Global's ability to convert its cash distributions to United States dollars or other freely convertible currencies, or to move funds offshore from these countries. Furthermore, the central bank of any of these countries may have the authority to suspend, restrict or otherwise impose conditions on foreign exchange transactions or to approve distributions to foreign investors. Although PSEG Global generally seeks to structure power purchase contracts and other project revenue agreements to provide for payments to be made in, or indexed to, United States dollars or a currency freely convertible into United States dollars, its ability to do so in all cases may be limited.

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The ongoing transformation of the energy industry could have a negative effect on the combined company's businesses.

        The energy industry is undergoing major transformations. Increased competition from new or restructured suppliers could have a negative impact on the combined company's wholesale and retail sales. Increased competition also could erode the price of power and result in lower revenues, which in turn could affect the combined company's results of operations and cash flows. Additionally, the changing industry will expose the combined company's energy delivery and generation businesses to marketplace volatility that they have not historically been called upon to manage. These changes have significantly affected the whole industry and the manner in which its participants conduct their businesses. These changes are ongoing, and Exelon and PSEG cannot predict, and the combined company will not be able to predict, the future course of changes in laws and regulations, including changes resulting from market volatility and increased security concerns, or the ultimate effect that this changing regulatory environment will have on the combined company's businesses.

The combined company's businesses will depend on access to the capital markets.

        The combined company's businesses will be capital intensive and will depend on access to the capital markets to meet its capital resource requirements to the extent not provided by internally generated funds. The combined company also may need to access the capital markets to finance acquisitions. When necessary, the combined company may secure funds from external sources by issuing commercial paper and, as required, long-term debt securities. The ability to arrange debt financing, to refinance current maturities and early retirements of debt, and the costs of issuing new debt are dependent on:

•

credit availability from banks and other financial institutions;



•

maintenance of acceptable credit ratings;



•

investor confidence in the combined company and its subsidiaries;



•

general economic and capital market conditions; and



•

the success of current projects.

The combined company may make acquisitions that do not achieve the intended financial results.

        Exelon and PSEG currently expect that the combined company will opportunistically evaluate investment opportunities that fit the combined company's strategic objectives and improve the combined company's financial performance and cash flows. The combined company's future financial performance will depend in part upon a variety of factors related to these investments, including its ability to successfully integrate them into existing operations. These new investments, as well as Exelon's and PSEG's existing investments, may not achieve the financial performance that Exelon and PSEG expect.

Market performance will affect the combined company's decommissioning trust funds and benefit plan asset values.

        The performance of the capital markets will affect the value of the assets that are held in trust to satisfy the combined company's future obligations under its pension and post-retirement benefit plans and to decommission nuclear generating plants. A decline in the market value of those assets, as was experienced from 2000 to 2002, may increase the combined company's funding requirements for these obligations.

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The combined company's results of operations and cash flows may be affected by its ability to divest unprofitable or under-performing businesses.

        Exelon and PSEG currently, and the combined company will, pursue opportunities to sell businesses and assets that either do not meet the strategic objectives of the combined company or are unprofitable. The combined company may incur significant expenses in divesting these businesses. The combined company also may be unable to implement successfully this strategy for a number of reasons, including an inability to locate appropriate buyers or to negotiate acceptable terms for the transactions. In addition, the amounts that the combined company may realize from a divestiture are subject to fluctuating market conditions that may contribute to pricing and other terms that are materially different than expected and could result in a loss on the sale. Timing of any divestitures may positively or negatively affect the combined company's results of operations and cash flows.

War and acts and threats of terrorism may adversely affect the combined company's results of operations, the combined company's ability to raise capital and its future growth.

        Exelon and PSEG do not fully know the impact that any future terrorist attacks may have on the industry in general and on the combined company in particular. In addition, any retaliatory military strikes or sustained military campaign may affect the combined company's operations in unpredictable ways, such as changes in insurance markets and disruptions of fuel supplies and markets, particularly oil. The possibility alone that infrastructure facilities, such as electric generation, electric and gas transmission and distribution facilities, would be direct targets of, or indirect casualties of, an act of terror may affect the combined company's operations. Additionally, the continuing military activity in Iraq and other wars may have an adverse effect on the economy in general. A lower level of economic activity might result in a decline in energy consumption, which may adversely affect the combined company's revenues or restrict its future growth. Instability in the financial markets as a result of terrorism or war may affect the combined company's stock price and its ability to raise capital.

The combined company's financial performance and cash flows are affected by its ability to manage costs for security and liability insurance.

        Security.    As a result of the events of September 11, 2001, the electric industry has developed additional security guidelines. The electric industry, through the North American Electric Reliability Council, developed physical security guidelines, which were accepted by the United States Department of Energy and which may become mandatory through regulation or legislation. The gas industry, through the American Gas Association, developed physical security guidelines that were accepted by the United States Department of Transportation.

        Exelon Generation and PSEG Power have also initiated security measures, including those mandated by the NRC, to safeguard its employees and critical operations and is actively participating in industry initiatives to identify methods to maintain the reliability of its energy production and delivery systems. These security measures have resulted in and are expected to continue to result in increased costs. On a continuing basis, Exelon Generation and PSEG Power evaluate enhanced security measures at certain critical locations, enhanced response and recovery plans and assessing long-term design changes and redundancy measures. Additionally, the energy industry is working with governmental authorities to ensure that emergency plans are in place and critical infrastructure vulnerabilities are addressed in order to maintain the reliability of the country's energy systems. These measures will involve additional expense to develop and implement.

        Insurance.    As a result of significant changes in the insurance marketplace, due in part to the September 11, 2001 terrorist acts, the coverage available and the limits under property damage and liability insurance that the combined company buys may be less than those that Exelon and PSEG could obtain in the past, and the recovery for losses due to terrorists acts may be limited. The

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combined company will be self-insured for losses that exceed the amount of insurance it maintains. A claim that exceeds the amounts available under the combined company's property damage and liability insurance would negatively affect its results of operations. The combined company will not carry any form of business interruption insurance other than replacement power coverage for its nuclear operations. Damage to the combined company's delivery facilities may disrupt their delivery services and significantly and adversely affect the combined company's results of operations. Any claim resulting from a nuclear accident exceeding the amounts available under the combined company's nuclear liability insurance and other sources for payment of claims or resulting in a material amount of retrospective assessments of premiums could have a material adverse effect on the combined company's results of operations and its financial condition.

The combined company may incur substantial costs to fulfill its obligations related to environmental matters.

        Subsidiaries of Exelon and PSEG are subject to extensive environmental regulation by local, state and federal authorities. These laws and regulations affect the manner in which Exelon and PSEG and their subsidiaries conduct their operations and make capital expenditures. Further, such laws and regulations are subject to future changes that may result in increased compliance costs. For example, during 2005 the United States Environmental Protection Agency is expected to finalize more stringent nitrogen oxide (NOx) and sulfur dioxide (SO2) regulation for the eastern United States that will take effect in approximately 2010. Proposed EPA mercury regulations are also expected to be finalized and implemented on roughly the same timeline. Subsidiaries of Exelon and PSEG are subject to liability under environmental laws for the costs of remediating environmental contamination of property now or formerly owned by them and of property contaminated by hazardous substances they generated. Remediation activities associated with manufactured gas plant operations for subsidiaries of Exelon and PSEG will be one source of such costs. Also, subsidiaries of Exelon and PSEG are currently involved in a number of proceedings relating to sites where hazardous substances have been deposited and may be subject to additional proceedings in the future. In addition, most of PSEG's generating facilities are located in the State of New Jersey. In particular, New Jersey's environmental programs are generally considered to be more stringent in comparison to similar programs in other states. Therefore, there may be instances where the facilities located in New Jersey are subject to more stringent and, therefore, more costly pollution control requirements than competitive facilities in other states. The Salem nuclear generating facility has a permit from the New Jersey Department of Environment Protection allowing for the continued operation of the Salem facility with its existing cooling water system. That permit expires in July 2006. The NJDEP, in anticipation of PSEG's application to renew the permit for Salem, has advised PSEG that it strongly recommends that cooling water intake flow at the Salem facility be reduced commensurate with closed cycle cooling. The application of Federal Water Pollution Control Act Section 316(b) regulations published in 2004 could, as one option, require the installation of structures at the Salem facility to reduce cooling water intake commensurate with closed cycle cooling, which would result in material costs of compliance for the combined company. The regulations under Section 316(b) of the FWPCA could also result in material costs of compliance at other generating facilities of the combined company.

Exelon and PSEG retain contingent liabilities in connection with asset sales.

        Exelon and PSEG have each divested a number of assets over the last three years. We have entered into a number of agreements for the sale of assets that include provisions whereby we are required to:

•

retain specified preexisting liabilities such as for taxes and pensions;



•

indemnify the buyers against specified risks, including the inaccuracy of representations and warranties we made; and



•

require payments to the buyers depending on the outcome of post-closing adjustments, audits or other reviews.

        Many of these contingent liabilities can remain open for extended periods of time after the sales are closed. Depending on the extent to which the buyers may ultimately seek to enforce their rights under these contractual provisions, and the resolution of any disputes we may have concerning them, these liabilities could have a material adverse effect on our financial condition, liquidity, cash flow and results of operations.

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FORWARD-LOOKING STATEMENTS

        We have made forward-looking statements in this joint proxy statement/prospectus, including in the documents that are incorporated by reference into this joint proxy statement/prospectus, that are subject to risks and uncertainties. These statements are based on the current expectations of each company's management. Generally, forward-looking statements include information concerning possible or assumed future actions, events or results of operations of Exelon, PSEG and the combined company. Forward-looking statements include the information in this joint proxy statement/prospectus regarding:

•

management forecasts, projections and estimates;



•

liquidity and the ability to access the capital and credit markets;



•

regulatory matters;



•

efficiencies/cost avoidance;



•

cost savings;



•

income and margins;



•

earnings per share;



•

economies of scale;



•

combined operations;



•

the economy;



•

future economic performance;



•

conditions to, and the timetable for, completing the merger;



•

future acquisitions and dispositions;



•

litigation;



•

potential and contingent liabilities;



•

management's plans;



•

business portfolios;



•

taxes; and



•

merger and integration-related expenses.

        These statements may be preceded by, followed by or include the words "may," "will," "should," "could," "would," "potential," "possible," "believes," "expects," "anticipates," "intends," "plans," "estimates," "hopes" or similar expressions. We claim the protection of the safe harbor for forward-looking statements contained in the Private Securities Litigation Reform Act of 1995 for all forward-looking statements.

        Forward-looking statements are not guarantees of performance. You should understand that the following important risks, in addition to those discussed in "Risk Factors" above and elsewhere in this joint proxy statement/prospectus, and in the documents which are incorporated by reference into this joint proxy statement/prospectus, could affect the future results of Exelon and PSEG, and of the combined company after completion of the merger, and could cause those results or other outcomes to differ materially from those expressed or implied in our forward-looking statements:

•

Exelon and PSEG may be unable to obtain shareholder approvals required for completion of the merger;

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•

Exelon and PSEG may be unable to obtain regulatory approvals required for completion of the merger, or required regulatory approvals may delay the merger or result in the imposition of conditions that could have a material adverse effect on the combined company or cause the companies to abandon the merger;



•

conditions to the closing of the merger may not be satisfied;



•

an unsolicited offer of another company to acquire assets or capital stock of Exelon or PSEG could interfere with the merger;



•

problems may arise in successfully integrating the businesses of the companies, which may result in the combined company not operating as effectively and efficiently as expected;



•

the combined company may be unable to achieve cost-cutting synergies or it may take longer than expected to achieve those synergies;



•

the merger may involve unexpected costs or unexpected liabilities, or the effects of purchase accounting may be different from Exelon's and PSEG's expectations;



•

the credit ratings of the combined company or its subsidiaries may be different from what Exelon and PSEG expect;



•

the businesses of Exelon and PSEG may suffer as a result of uncertainty surrounding the merger;



•

Exelon and PSEG may experience more difficulties than expected in achieving operating improvements at jointly owned nuclear generating facilities;



•

Exelon and PSEG may not realize the values expected to be obtained for properties expected or required to be divested;



•

the industry may be subject to future regulatory or legislative actions that could further limit revenues or cost recoveries or impose additional costs or otherwise adversely affect Exelon, PSEG or the combined company;



•

Exelon and PSEG may be adversely affected by other economic, business and competitive factors and volatility of energy and commodities markets;



•

changes in accounting policies, practices or their interpretations; and



•

the factors described in Exelon's and PSEG's reports filed with the SEC.

        Because forward-looking statements are subject to assumptions and uncertainties, actual results may differ materially from those expressed or implied by such forward-looking statements. Shareholders are cautioned not to place undue reliance on such statements, which speak only as of the date of this joint proxy statement/prospectus or the date of any document incorporated by reference.

        All subsequent written and oral forward-looking statements concerning the merger or other matters addressed in this joint proxy statement/prospectus and attributable to Exelon or PSEG or any person acting on either company's behalf are expressly qualified in their entirety by the cautionary statements contained or referred to in this section. Except to the extent required by applicable law or regulation, neither Exelon nor PSEG undertakes any obligation to publicly release any revisions or updates to such forward-looking statements to reflect events or circumstances after the date of this joint proxy statement/prospectus or to reflect the occurrence of unanticipated events.

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THE COMPANIES

Exelon Corporation
10 South Dearborn Street—37th Floor
P.O. Box 805379
Chicago, Illinois 60680-5379
(312) 394-7398
Internet address: www.exeloncorp.com

        Exelon Corporation, a registered public utility holding company under the Public Utility Holding Company Act of 1935, as amended, through its subsidiaries, operates in three business segments—Energy Delivery, Generation and Enterprises—as described below. In addition to Exelon's three business segments, Exelon Business Services Company, a subsidiary of Exelon, provides Exelon and its subsidiaries with financial, human resource, legal, information technology, supply management and corporate governance services. Exelon was incorporated in Pennsylvania in February 1999.

        Energy Delivery.    Exelon's energy delivery business consists of the purchase and sale of electricity and distribution and transmission services by Commonwealth Edison Company in northern Illinois and by PECO Energy Company in southeastern Pennsylvania and the purchase and sale of natural gas and distribution services by PECO in the Pennsylvania counties surrounding the City of Philadelphia. ComEd's retail service territory has an area of approximately 11,300 square miles and an estimated population of 8 million. The service territory includes the City of Chicago, an area of about 225 square miles with an estimated population of 3 million. ComEd has approximately 3.76 million customers. PECO's retail service territory has an area of approximately 2,100 square miles and an estimated population of 3.8 million. PECO provides electric delivery service in an area of approximately 2,000 square miles, with a population of approximately 3.7 million, including 1.5 million in the City of Philadelphia. Natural gas service is supplied in an area of approximately 1,900 square miles in southeastern Pennsylvania adjacent to the city of Philadelphia, with a population of approximately 2.3 million. PECO delivers electricity to approximately 1.5 million customers and natural gas to approximately 460,000 customers.

        Generation.    Exelon's generation business consists of the owned and contracted for electric generating facilities and energy marketing operations of Exelon Generation Company, a 49.5% interest in two power stations in Mexico and the competitive retail sales business of Exelon Energy Company.

        Generating Facilities. At December 31, 2004, Exelon Generation owned generation assets in the Midwest, Mid-Atlantic, Southern and Northeast regions and the state of Texas with a net capacity of 26,756 MWs, including 16,751 MWs of nuclear capacity. Exelon Generation controls another 8,701 MWs of capacity in the Midwest, Southeast regions and South Central regions of the state of Texas through long-term contracts.

        Energy Marketing Operations. Exelon Generation's wholesale marketing unit, Power Team, a major wholesale marketer of energy, uses Exelon Generation's energy generation portfolio, transmission rights and expertise to ensure delivery of energy to Exelon Generation's wholesale customers under long-term and short-term contracts, including the load requirements of ComEd and PECO. In addition, Power Team markets energy in the wholesale bilateral and spot markets.

        Retail Sale. Exelon Energy Company became part of Exelon Generation effective as of January 1, 2004. Exelon Energy provides retail electric and gas services as an unregulated retail energy supplier in Illinois, Michigan, Ohio, Pennsylvania and Kentucky.

        Enterprises.    Exelon's enterprise business is comprised of infrastructure and electrical contracting services of Exelon Enterprises Company, LLC and other investments weighted towards the communications and energy services industries. During 2004 and 2003, Enterprises exited a significant number of businesses and investments. Exelon plans to divest or wind-down the remaining assets of Enterprises during 2005.

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Public Service Enterprise Group Incorporated
80 Park Plaza
P.O. Box 1171
Newark, New Jersey 07101-1171
(973) 430-7000
Internet address: www.pseg.com

        Public Service Enterprise Group Incorporated is an exempt public utility holding company under PUHCA. PSEG has four principal direct wholly-owned subsidiaries: Public Service Electric and Gas Company, PSEG Power LLC, PSEG Energy Holdings LLC and PSEG Services Corporation. PSEG was incorporated under the laws of the State of New Jersey in 1985.

        PSE&G.    PSE&G is an operating public utility company engaged principally in the transmission and distribution of electric energy and gas service in New Jersey. PSE&G provides electric and gas service in areas of New Jersey in which approximately 5.5 million people, about 70% of the State's population, reside. PSE&G's electric and gas service area is a corridor of approximately 2,600 square miles running diagonally across New Jersey from Bergen County in the northeast to an area below the city of Camden in the southwest. The greater portion of this area is served with both electricity and gas, but some parts are served with electricity only and other parts with gas only. This heavily populated, commercialized and industrialized territory encompasses most of New Jersey's largest municipalities, including its six largest cities—Newark, Jersey City, Paterson, Elizabeth, Trenton and Camden—in addition to approximately 300 suburban and rural communities. This service territory contains a diversified mix of commerce and industry, including major facilities of many nationally prominent corporations. PSE&G's load requirements are almost evenly split among residential, commercial and industrial customers.

        PSEG Power.    PSEG Power is a multi-regional, wholesale energy supply company that integrates its generating asset operations with its wholesale energy, fuel supply, energy trading and marketing and risk management function through three principal direct wholly-owned subsidiaries: PSEG Nuclear LLC, PSEG Fossil LLC and PSEG Energy Resources & Trade LLC.

        PSEG Fossil. PSEG Fossil has a direct ownership interest in twelve generating stations in New Jersey, two in Pennsylvania, one in New York, two in Connecticut, one in Ohio and one in Indiana. PSEG Fossil also has an ownership interest in one hydroelectric pumped storage facility in New Jersey. PSEG Fossil uses coal, natural gas and oil for electric generation. These fuels are purchased through various contracts and in the spot market and represent a significant portion of PSEG Power's working capital requirements. Changes in the prices of these fuel sources can impact PSEG Power's costs and working capital requirements. The majority of PSEG Power's fossil generating stations obtain their fuel supply from within the United States.

        PSEG Nuclear. PSEG Nuclear has an ownership interest in five nuclear generating units and operates three of them: the Salem Nuclear Generating Station, Units 1 and 2, each owned 57.41% by Nuclear and 42.59% by Exelon Generation, and the Hope Creek Nuclear Generating Station, which is 100% owned by PSEG Nuclear. Exelon Generation operates the Peach Bottom Atomic Power Station Units 2 and 3, each of which is 50% owned by PSEG Nuclear.

        PSEG ER&T. PSEG ER&T purchases virtually all of the capacity and energy produced by PSEG Fossil and PSEG Nuclear. In conjunction with these purchases, PSEG ER&T uses commodity and financial instruments designed to cover estimated commitments for the New Jersey Basic Generation Service auction and other bilateral contract agreements. PSEG ER&T also markets electricity, capacity, ancillary services and natural gas products on a wholesale basis. PSEG ER&T is a fully integrated wholesale energy marketing and trading organization that is active in the long-term and spot wholesale energy markets.

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        PSEG Energy Holdings.    PSEG Energy Holdings is a New Jersey limited liability company and is the successor to PSEG Energy Holdings Inc., which was originally incorporated in 1989. PSEG Energy Holdings has two principal direct wholly-owned subsidiaries, PSEG Global LLC and PSEG Resources LLC. PSEG Global has pursued investment opportunities in electric generation, transmission and distribution facilities and is engaged in power production and distribution in selected domestic and international markets. PSEG Resources invests in energy-related financial transactions and manages a diversified portfolio of assets. Upon completion of the merger, the combined company intends to pursue opportunities to sell certain of PSEG Global's investments that do not meet the strategic objectives of the combined company.

        PSEG Services.    PSEG Services provides management and administrative services to PSEG and its subsidiaries. These include accounting, legal, communications, human resources, information technology, treasury and financial, investor relations, shareholder services, real estate, insurance, risk management, tax, library and information services, security, corporate secretarial and certain planning, budgeting and forecasting services. PSEG Services charges PSEG and its subsidiaries for the cost of work performed and services provided pursuant to the terms and conditions of intercompany service agreements.

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CHAPTER TWO
INFORMATION ABOUT THE ANNUAL MEETINGS AND VOTING
 
THE EXELON ANNUAL MEETING

        The Exelon board of directors is using this joint proxy statement/prospectus to solicit proxies from the holders of Exelon common stock for use at the annual meeting of Exelon's shareholders. Exelon is first mailing this joint proxy statement/prospectus and accompanying proxy card to Exelon shareholders on or about [    •    ], 2005.

Date, Time and Place of Annual Meeting

        The Exelon annual meeting of shareholders will be held on [    •    ], 2005 at [    •    ], local time at [    •    ].

Purpose of the Annual Meeting

        The purpose of the annual meeting is to take action upon the following:

•

a proposal to approve the issuance of shares of Exelon common stock as contemplated by the merger agreement;



•

the election of five Class II directors: Edward A. Brennan, Bruce DeMars, Nelson A. Diaz, John W. Rowe and Ronald Rubin, each for a three year term;



•

a proposal to approve the amendment to Exelon's Amended and Restated Articles of Incorporation to increase the number of authorized shares of Exelon common stock from 1,200,000,000 to 2,000,000,000;



•

a proposal to ratify PricewaterhouseCoopers LLP as Exelon's independent accountants for the year 2005;



•

a proposal to approve the Exelon Corporation 2006 Long-Term Incentive Plan;



•

a proposal to approve the Exelon Corporation Employee Stock Purchase Plan for Unincorporated Subsidiaries;



•

any proposal of the Exelon board of directors to adjourn or postpone the Exelon annual meeting; and



•

any other business that properly comes before the annual meeting and any adjournment or postponement thereof.

Record Date for the Annual Meeting

        The Exelon board of directors has fixed the close of business on [    •    ], 2005 as the record date for determination of shareholders entitled to notice of and to vote at the Exelon annual meeting.

Outstanding Shares

        As of [    •    ], 2005, the record date for the Exelon annual meeting, there were approximately [    •    ] shares of Exelon common stock outstanding.

Shares Entitled to Vote

        Shares entitled to vote at the Exelon annual meeting are shares of Exelon common stock held as of the close of business on the record date, [    •    ], 2005. Each shareholder is entitled to one vote at the Exelon annual meeting for each share of Exelon common stock held by that shareholder at the

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close of business on the record date. Shares of Exelon common stock held by Exelon in its treasury are not voted.

Quorum, Abstentions and Broker Non-Votes

        A quorum of Exelon shareholders is necessary to permit a particular matter to be considered and acted upon at the meeting. The presence in person or by proxy at the annual meeting of holders of issued and outstanding shares of Exelon common stock entitled to cast at least a majority of the votes that all shareholders are entitled to cast on a particular matter constitutes a quorum. Broker non-votes (so long as such shares are voted on the director proposal or proposal to ratify Exelon's independent accountants) and abstentions count as present for establishing a quorum. Shares held by Exelon in its treasury do not count towards a quorum. A broker non-vote occurs on an item when the broker is not permitted to vote on that item without instruction from the beneficial owner of the shares of Exelon common stock and the beneficial owner gives no instruction as to voting of the shares. Under New York Stock Exchange rules, your broker or bank does not have discretionary authority to vote your shares on the proposal to issue shares of Exelon common stock as contemplated by the merger agreement, the proposal to amend Exelon's Amended and Restated Articles of Incorporation to increase the number of authorized shares of Exelon common stock, the proposal to approve the Exelon Corporation 2006 Long-Term Incentive Plan or the proposal to approve the Exelon Corporation Employee Stock Purchase Plan for Unincorporated Subsidiaries. Without your voting instructions on those items, a broker non-vote will occur.

Vote Required

        The proposals require different percentages of votes in order to approve them:

•

approval of the proposal to issue shares of Exelon common stock as contemplated by the merger agreement requires the affirmative vote of at least a majority of the votes cast by holders of shares of Exelon common stock present in person or by proxy and entitled to vote so long as the total vote cast on the proposal represents at least a majority of the shares of Exelon common stock entitled to vote on the proposal, assuming a quorum is present;



•

directors are elected by a plurality vote, with the five nominees who receive the most votes elected, assuming a quorum is present;



•

approval of the proposal to amend Exelon's Amended and Restated Articles of Incorporation to increase the number of authorized shares of Exelon common stock from 1,200,000,000 to 2,000,000,000 requires the affirmative vote of at least a majority of the votes cast by holders of shares of Exelon common stock present in person or by proxy and entitled to vote, assuming a quorum is present;



•

approval of the proposal to approve the Exelon Corporation 2006 Long-Term Incentive Plan and the Exelon Corporation Employee Stock Purchase Plan for Unincorporated Subsidiaries requires the affirmative vote of at least a majority of the votes cast by holders of shares of Exelon common stock present in person or by proxy and entitled to vote so long as the total vote cast on the proposal represents at least a majority of the shares of Exelon common stock entitled to vote on the proposal, assuming a quorum is present;



•

approval of a proposal by the Exelon board of directors to adjourn or postpone the meeting requires the affirmative vote a majority of the votes cast by holders of shares of Exelon common stock present in person or by proxy at the meeting, whether or not a quorum is present; and



•

approval of all other proposals requires the affirmative vote of a majority of the votes cast by holders of shares of Exelon common stock present in person or by proxy and entitled to vote, assuming a quorum is present.

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        Abstentions and broker non-votes are not counted as votes cast on a proposal.

Shares Beneficially Owned by Exelon Directors and Officers

        Exelon directors and officers beneficially owned [    •    ] shares of Exelon common stock on [    •    ], 2005 the record date for the Exelon annual meeting. These shares represent in total [    •    ]% of the total voting power of Exelon's voting securities outstanding and entitled to vote as of [    •    ], 2005. Exelon currently expects that Exelon's directors and officers will vote their shares in favor of the share issuance proposal, although none of them has entered into any agreements obligating them to do so.

Voting at the Annual Meeting

        If you are a shareholder of record, you may vote in person by ballot at the Exelon annual meeting or by submitting a proxy. Exelon recommends you submit your proxy even if you plan to attend the annual meeting. If you attend the annual meeting, you may vote by ballot, thereby canceling any proxy previously submitted.

        Voting instructions are included on your proxy card. If you properly give your proxy and submit it to Exelon in time to vote, one of the individuals named as your proxy will vote your shares as you have directed. You may vote for or against the proposals or abstain from voting.

How to Vote by Proxy

        By Telephone or Internet.    If you are a shareholder of record, you can submit your proxy by telephone by calling the toll-free telephone number on your proxy card (877) 779-8683 or by Internet by accessing the website identified on your proxy card www.eproxyvote.com/exc. Telephone and Internet voting are available 24 hours a day and will be accessible until [    •    ] p.m. on [    •    ], 2005. Exelon's telephone and Internet voting procedures are designed to authenticate shareholders by using individual control numbers. If you hold your shares through a bank, broker, custodian or other recordholder, please refer to your proxy card or the voter information form provided by your bank, broker, custodian or other recordholder for information on Internet voting. If you submit your proxy by telephone or Internet, please do not mail your proxy card. If you are located outside the United States, Canada and Puerto Rico, see your proxy card or other materials for additional instructions with respect to voting by telephone.

        By Mail.    If you are a shareholder of record and choose to submit your proxy by mail, please complete each proxy card you receive, date and sign it, and return it in the prepaid envelope which accompanied that proxy card. If you hold your shares through a bank, broker, custodian or other recordholder, please refer to your proxy card or the voter information form provided to you by your bank, broker, custodian or other recordholder.

Proxies without Instruction

        If you are a shareholder of record and submit your proxy but do not make specific choices, your proxy will follow the Exelon board of directors' recommendations and your shares will be voted:

•

"FOR" the proposal to approve the issuance of shares of Exelon common stock as contemplated by the merger agreement;



•

"FOR" the proposal to elect the directors named in the director proposal;



•

"FOR" the proposal to approve the amendment to Exelon's Amended and Restated Articles of Incorporation to increase the number of authorized shares of Exelon common stock;