Marathon Petroleum says partnership will buy MarkWest for $14.69B in cash and stock

A partnership run by Marathon Petroleum will spend $14.69 billion to buy MarkWest Energy Partners, a company that splits natural gas into other fuels.

The combined company will have a market capitalization of $21 billion and tie up Marathon's huge pipeline network with the refiner.

The cash-and-stock deal values MarkWest units at $78.64 each. The companies said the purchase includes $4.2 billion in debt held by MarkWest. The companies value the deal at $20 billion and expect it to be completed during the fourth quarter. Denver's MarkWest will become a unit of MPLX LP, a midstream partnership created by Marathon Petroleum.

MarkWest is among the biggest natural gas processors in the U.S. and is active in major shale plays line Marcellus in the Northeast and Utica on its western border.