On June 5, 2009, MarkWest Energy Partners, L.P. (the "Partnership") and MarkWest Energy Operating Company, L.L.C. (the "Operating Company") entered into an Underwriting Agreement (the "Underwriting Agreement") with Morgan Stanley & Co. Incorporated ("Morgan Stanley"), with respect to the issuance and sale in an underwritten public offering (the "Common Unit Offering") by the Partnership of 2,900,000 common units representing limited partner interests (the "Common Units") at $18.15 per common unit. The Partnership has granted Morgan Stanley a 30-day option to purchase a maximum of 435,000 additional common units to cover over-allotments, if any. The Common Units to be sold in the Common Unit Offering were registered under the Securities Act of 1933, as amended (the "Securities Act"), pursuant to a registration statement on Form S-3 (File No. 333-157883). The closing of the Common Unit Offering is expected to occur on June 10, 2009. Legal opinions related to the Common Units are filed as Exhibits 5.1 and 8.1 to this Current Report on Form 8-K.

The Partnership intends to use the net proceeds from the Common Unit Offering of approximately $50.3 million, excluding offering expenses, to partially fund its growth capital budget. Pending that use, the Partnership intends to apply a portion of the net proceeds to pay down borrowings under its revolving credit facility.

The foregoing description is a brief summary of the Underwriting Agreement and does not purport to be a complete statement of the parties' rights and obligations under the Underwriting Agreement. The foregoing description is qualified in its entirety by reference to the full text of the Underwriting Agreement, which is filed as Exhibit 1.1 to this Current Report on Form 8-K and is incorporated by reference herein.

On June 4, 2009, the Partnership issued a press release announcing the Common Unit Offering. A copy of the press release is furnished as Exhibit 99.2 hereto.

On June 5, 2009, the Partnership issued a press release announcing the pricing of the Common Unit Offering. A copy of the press release is furnished as Exhibit 99.2 hereto.

The information contained in this Item 7.01 shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or incorporated by reference in any filing under the Securities Act or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

Cautionary Statements

This filing includes "forward-looking statements." All statements other than statements of historical facts included or incorporated herein may constitute forward-looking statements. Actual results could vary significantly from those expressed or implied in such statements and are subject to a number of risks and uncertainties. Although we believe that the expectations reflected in the forward-looking statements are reasonable, we can give no assurance that such expectations will prove to be correct. The forward-looking statements involve risks and uncertainties that affect our operations, financial performance, and other factors as discussed in our filings with the Securities and Exchange Commission. Among the factors that could cause results to differ materially are those risks discussed in the periodic reports we file with the SEC, including our Annual Report on Form 10-K, for the year ended December 31, 2008, and our Quarterly Report on Form 10-Q, for the three months ended March 31, 2009, as filed with the SEC. You are urged to carefully review and consider the cautionary statements and other disclosures made in those filings, specifically those under the heading "Risk Factors."

(d) Exhibits.

Exhibit No.                            Description of Exhibit
1.1            Underwriting Agreement dated as of June 5, 2009 among MarkWest Energy
               Partners, L.P., MarkWest Energy Operating Company, L.L.C., and Morgan
               Stanley & Co. Incorporated.
5.1            Opinion of Vinson & Elkins
8.1            Opinion of Vinson & Elkins, relating to tax matters
23.1           Consent of Vinson & Elkins (included in Exhibit 5.1)
23.2           Consent of Vinson & Elkins (included in Exhibit 8.1)
99.1           Press release dated June 4, 2009, announcing public offering of common
               units.
99.2           Press release dated June 5, 2009, announcing pricing of public offering
               of common units.