[Vinson & Elkins L.L.P. Letterhead]

Exhibit 8.1

March 22, 2005

Energy Transfer Partners, L.P.

2838 Woodside Street

Dallas, Texas 75204

RE: ENERGY TRANSFER PARTNERS, L.P. REGISTRATION STATEMENT ON FORM S-3

Ladies and Gentlemen:

We have acted as counsel for Energy Transfer Partners, L.P., a Delaware limited partnership (the “Partnership”) with respect to certain legal matters in connection with the filing with the Securities and Exchange Commission (the “Commission”) of a registration statement (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), regarding the offer and sale by certain unitholders of the Partnership of up to 6,296,294 common units representing limited partner interests in the Partnership. We have also participated in the preparation of a Prospectus (the “Prospectus”) contained in the Registration Statement on Form S-3 to which this opinion is an exhibit. In connection therewith, we prepared the discussion (the “Discussion”) set forth under the caption “Material Tax Considerations” in the Prospectus.

All statements of legal conclusions contained in the Discussion, unless otherwise noted, are our opinion with respect to the matters set forth therein as of the effective date of the Prospectus, qualified by the limitations contained in the Discussion. In addition, we are of the opinion that the Discussion with respect to those matters as to which no legal conclusions are provided is an accurate discussion of such federal income tax matters (except for the representations and statements of fact of the Partnership and its general partner, included in the Discussion, as to which we express no opinion).

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to the use of our name in the Registration Statement. This consent does not constitute an admission that we are “experts” within the meaning of such term as used in the Securities Act.

Very truly yours,

/s/ VINSON & ELKINS L.L.P.

VINSON & ELKINS L.L.P.