Unitholders of MarkWest Energy Partners LP on Dec. 1 approved the company's sale to MPLX LP , a master limited partnership of Marathon Petroleum Corp.

About 80 percent of the unitholders voted in favor of the cash-and-stock deal, which values MarkWest Energy at $10.38 billion, the companies said in a joint statement.

MarkWest shares were down 5.3 percent at $45.44, while those of MPLX plunged 14.3 percent to $36.81.

The approval comes after Marathon Petroleum raised the cash portion of its offer for the second time by $210 million to $1.28 billion for the company.

MarkWest will become a wholly owned unit of MPLX and the two companies are expected to generate a mid-20 percent compound annual distribution growth rate through 2019.

John Fox, a MarkWest unitholder, had opposed the deal earlier in November, saying it would lead to a big cut in cash distributions to unitholders.

The deal is expected to close on Dec. 4.

Up to Monday's close, MarkWest shares had fallen 30 percent since July 13, when the deal was announced, while MPLX shares are down 27 percent.