Organization and Basis of Presentation

12 Months Ended

Dec. 31, 2011

Organization and Basis of Presentation

Organization and Basis of Presentation

1. Organization and Basis of Presentation

        MarkWest Energy Partners, L.P. ("MarkWest Energy Partners") was formed in January 2002 as a Delaware limited partnership. In February 2008, MarkWest Energy Partners completed its Merger with MarkWest Hydrocarbon, Inc. (the "Corporation" or "MarkWest Hydrocarbon") and MWEP, L.L.C, whereby MarkWest Hydrocarbon became a wholly-owned subsidiary of MarkWest Energy Partners. MarkWest Energy Partners and its majority-owned subsidiaries (collectively, the "Partnership") are engaged in the gathering, transportation and processing of natural gas; the transportation, fractionation, marketing and storage of NGLs and the gathering and transportation of crude oil. The Partnership has established a significant presence in the Southwest through strategic acquisitions and strong organic growth opportunities stemming from those acquisitions. The Partnership is also the largest processor and fractionator of natural gas in the Appalachian Basin and continues to expand this position through the growth of its operations in the Marcellus Shale. Finally, the Partnership owns a crude oil transportation pipeline in Michigan. The Partnership's principal executive office is located in Denver, Colorado.

        The Partnership's consolidated financial statements include all majority-owned or majority-controlled subsidiaries. In addition, MarkWest Liberty Midstream and MarkWest Pioneer, variable interest entities for which the Partnership has been determined to be the primary beneficiary, are included in the consolidated financial statements. Effective December 31, 2011, the Partnership acquired the remaining 49% interest of MarkWest Liberty Midstream. As a result, as of December 31, 2011, MarkWest Liberty Midstream is not a variable interest entity but is consolidated as a wholly-owned subsidiary (see Note 4 for further discussion of MarkWest Pioneer and MarkWest Liberty Midstream). For non-wholly-owned subsidiaries, the interests owned by third parties have been recorded as Non-controlling interest in consolidated subsidiaries in the accompanying Consolidated Balance Sheets. All significant intercompany investments, accounts and transactions have been eliminated. Investments in which the Partnership exercises significant influence but does not control, or is not the primary beneficiary, are accounted for using the equity method. The accompanying consolidated financial statements include the accounts of the Partnership and have been prepared in accordance with GAAP.