A partnership controlled by Marathon Petroleum Corp. MPC 7.87 % , a refinery and pipeline company, will buy MarkWest Energy Partners LP for $15.8 billion in one of the biggest oil-patch deals since crude prices began to slump last summer. The deal will marry Marathon’s oil pipeline network with MarkWest’s business separating natural gas into fuels such as propane and ethane. The combined company would have a market capitalization of $21 billion, making it the fourth-largest master limited partnership. These partnerships, which typically own infrastructure like pipelines that earn steady revenue from long-term contracts, have fared better than traditional drilling companies during the energy downturn but still have faced headwinds. Shares of MPLX closed 15% lower to $59, while shares of MarkWest rose nearly 14% to $68. Shares of Marathon Petroleum Corp. rose 7.9%. The deal is the latest consolidation between […]