Exhibit 8.1

2001 ROSS AVENUE DALLAS, TEXAS 75201-2980   TEL +1 214.953.6500 FAX +1 214.953.6503 www.bakerbotts.com AUSTIN BEIJING DALLAS DUBAI HONG KONG HOUSTON LONDON MOSCOW NEW YORK RIYADH WASHINGTON

February 12, 2008

SemGroup Energy Partners, L.P.

Two Warren Place

6120 South Yale Avenue, Suite 500

Tulsa, Oklahoma 74136

Ladies and Gentlemen:

We have acted as counsel to SemGroup Energy Partners, L.P., a Delaware limited partnership (the “Partnership”), with respect to certain legal matters in connection with the offer and sale of common units representing limited partner interests in the Partnership. We have also participated in the preparation of a Registration Statement on Form S-1 and the amendments thereto (Commission File No. 333-148755) being collectively referred to herein as the “Registration Statement” to which this opinion is an exhibit. In connection therewith, we prepared the discussion (the “Discussion”) set forth under the caption “Material Tax Consequences” in the Registration Statement.

We hereby confirm that all statements of legal conclusions contained in the Discussion reflect the opinion of Baker Botts L.L.P. with respect to the matters set forth therein as of the effective date of the Registration Statement, subject to the assumptions, qualifications, and limitations set forth therein.

In providing this opinion, we have examined and are relying upon the truth and accuracy at all relevant times of the statements, covenants, and representations contained in (i) the Registration Statement, (ii) a representation letter provided to us by the Partnership in support of this opinion, and (iii) other information provided to us by the Partnership, the general partner of the Partnership, SemGroup Energy Partners G.P., L.L.C., and SemGroup, L.P.

We hereby consent to the filing of this opinion as Exhibit 8.1 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 within the category of persons whose consent is required under Section 7 of the Securities Act of 1933, as amended, or the rules and regulations of the Commission thereunder.

Very truly yours,

/s/ Baker Botts L.L.P.