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Exhibit 8.1

January 13, 2010

MarkWest Energy Partners, L.P.
1515 Arapahoe Street
Tower 2, Suite 700
Denver, Colorado 80202

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

Ladies and Gentlemen:

        We have acted as counsel to MarkWest Energy Partners, L.P. (the "Partnership"), a Delaware limited partnership, and MarkWest Energy Finance Corp. (the "Finance Corp"), a Delaware corporation, with respect to certain legal matters in connection with the preparation of the Registration Statement on Form S-3 (the "Registration Statement") filed with the Securities and Exchange Commission (the "Commission") on the date hereof and to which this opinion is an exhibit. The Registration Statement relates to the registration under the Securities Act of 1933, as amended (the "Securities Act"), of the offer and sale, from time to time, pursuant to Rule 415 under the Securities Act, of:

        (1)   common units representing limited partner interests in the Partnership;

        (2)   debt securities of the Partnership and the Finance Corp. (the "Debt Securities"); and

        (3)   guarantees of the Debt Securities by certain Partnership subsidiaries.

In connection therewith, we prepared the discussion (the "Discussion") set forth under the caption "Material Tax Consequences" in the Registration Statement.

        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 date hereof, 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 by 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 under the heading "Legal" therein. This consent does not, however, constitute an admission that we are "experts" within the meaning of such term as used in the Securities Act, or the rules and regulations of the Commission issued thereunder.

Very truly yours,

/s/ VINSON & ELKINS L.L.P.

Vinson & Elkins L.L.P.

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Exhibit 8.1