AMENDMENT NO. 1 TO AMENDED AND RESTATED LIMITED PARTNERSHIP AGREEMENT MARKWEST ENERGY PARTNERS, L.P

Exhibit 99.1

AMENDMENT NO. 1
TO
AMENDED AND RESTATED LIMITED PARTNERSHIP AGREEMENT
MARKWEST ENERGY PARTNERS, L.P.

        This Amendment No. 1 (" Amendment No. 1 ") to the AMENDED AND RESTATED LIMITED PARTNERSHIP AGREEMENT OF MARKWEST ENERGY PARTNERS, L.P. dated May 24, 2002, is agreed to, approved and made effective December 31, 2004, on behalf of MarkWest Energy Partners, L.P. (the " Partnership ") by Markwest Energy GP, L.L.C., the general partner of the Partnership (the " General Partner ").

W I T N E S S E T H

        WHEREAS, the General Partner, the Initial Limited Partner, the Organizational Limited Partner and the Limited Partners of the Partnership entered into that certain Amended and Restated Limited Partnership Agreement of the Partnership, dated as of May 24, 2002 (the " Partnership Agreement ");

        WHEREAS, the General Partner has agreed to contribute $1,660,000 towards the cost of constructing the New Cobb Plant as that term is defined below;

        WHEREAS, Section 13.1(d)(i) and (d)(iv) of the Partnership Agreement provides that the General Partner may amend any provision of the Partnership Agreement, without the approval of any Partner or Assignee, to reflect a change that, in the discretion of the General Partner, does not adversely affect the Limited Partners in any material respect or is required to effect the intent of the provisions of the Partnership Agreement;

        WHEREAS, acting pursuant to the power and authority granted t