Exhibit 5.1
Gentlemen:
We have acted as special counsel to Duncan Energy Partners L.P., a Delaware limited
partnership (the “Partnership”), in connection with the registration under the Securities
Act of 1933, as amended (the “Securities Act”), of the offering and sale of up to an
aggregate of 14,950,000 common units representing limited partner interests in the Partnership (the
“Common Units”) by the Partnership.
As the basis for the opinion hereinafter expressed, we have examined such statutes, including
the Delaware Revised Uniform Limited Partnership Act (the “Delaware Act”), regulations,
corporate records and documents, certificates of corporate and public officials, and other
instruments and documents as we have deemed necessary or advisable for the purposes of this
opinion. In making our examination, we have assumed that all signatures on documents examined by
us are genuine, the authenticity of all documents submitted to us as originals and the conformity
with the original documents of all documents submitted to us as certified, conformed or photostatic
copies.
Based on the foregoing and on such legal considerations as we deem relevant, we are of the
opinion that the Common Units, when issued and delivered on behalf of the Partnership against
payment therefore as described in the Partnership’s Registration Statement on Form S-1 (Commission
File No.
333-138371), as amended, relating to the Common Units (the “
Registration
Statement”), will be duly authorized, validly issued, fully paid and non-assessable.
We express no opinion other than as to the federal laws of the United States of America and
the Delaware Act. We hereby consent to the reference to us under the heading “Validity of the
Common Units” in the prospectus forming a part of the Registration Statement and to the filing of
this opinion as an exhibit to the Registration Statement. In giving this consent, we do not
thereby admit that we are included in the category of persons whose consent is required under
Section 7 of the Securities Act or the rules and regulations of the SEC issued thereunder.
Very truly yours,
