MarkWest Energy Partners, L.P. (MarkWest) is a master limited partnership engaged in the gathering, transportation, and processing of natural gas; the transportation, fractionation, marketing, and storage of natural gas liquids; and the gathering and transportation of crude oil. MarkWest has extensive natural gas gathering, processing, and transmission operations in the southwest, Gulf Coast, and northeast regions of the United States. MarkWest is a wholly owned subsidiary of MPLX LP, which is the master limited partnership formed by Marathon Petroleum Corporation.