MarkWest Energy Partners, L.P. (NYSE: MWE) (“MarkWest”) announced today that it has agreed to sell approximately 4,750,000 common units pursuant to a terms agreement under its equity distribution agreement with Citigroup Global Markets Inc. (the “Sales Agent”) for total gross proceeds of approximately $301.15 million. In addition, 250,000 common units will be sold by M&R MWE Liberty, LLC (the “Selling Unitholder”). MarkWest has granted the Sales Agent a 30-day option to purchase a maximum of 712,500 additional common units, and the Selling Unitholder has granted the Sales Agent a 30-day option to purchase a maximum of 37,500 additional common units. MarkWest intends to use the net proceeds of this offering for general partnership purposes, which may include, among other things paying or refinancing a portion of its outstanding indebtedness and funding working capital, its capital expenditure program or acquisitions. MarkWest will not receive any of the proceeds from the sale of common units by the Selling Unitholder. The offering is expected to close on December 23, 2013. The Sales Agent may offer the common units from time to time in one or more transactions on the New York Stock Exchange, in the over-the-counter market, through negotiated transactions or otherwise at market prices or negotiated prices. The offering is being made pursuant to an effective registration statement on Form S-3 previously filed with the Securities and Exchange Commission. Copies of the prospectus supplement, the accompanying base prospectuses and the free writing prospectus related to this offering may be obtained from Citigroup Global Markets Inc., c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717 (tel: 800-831-9146). This press release shall not constitute an offer to sell or the solicitation of an offer to buy, nor shall there be any sale of the securities described above in any state or jurisdiction in which such offer, solicitation, or sale would be unlawful prior to registration or qualification under the securities laws of such state or jurisdiction.