After weeks of stirring the pot, opponents of the MarkWest Energy Partners LP (NYSE: MWE) merger with MPLX LP (NYSE: MPLX) lost the war but won $605 million in cash concessions from MPLX parent Marathon Petroleum Corp. (NYSE: MPC).

At a special meeting Dec. 1, MarkWest unitholders approved a strategic combination with MPLX. MarkWest and MPLX said 80% of units voted at the special meeting were in favor of the merger.

The transaction, expected to close Dec. 4, means MarkWest, the second-largest processor of natural gas in the U.S. and largest processor and fractionator in the Marcellus and Utica shale plays, will become a wholly owned subsidiary of MPLX.

The combination creates one of the largest MLPs and is expected to generate a mid-20% compound annual distribution growth rate through 2019.

The deal, which is largely a unit-for-unit transaction, was worth about $15.7 billion when announced in July.

Former MarkWest CEO John Fox was among critics who raised concerns about the terms of the deal, including a 50% cut in distributions to MarkWest unitholders. The distributions may return to parity within three to five years.

“This is a pennies-on-the-dollar increase for a really bad deal,” Fox said on Nov. 17.

Fox and Brian O’Neill, founders of MarkWest Hydrocarbon, both said Nov. 20 that they intended to vote against the deal.

O’Neill said that unit exchange of 1.09 MPLX units for each MarkWest unit was unacceptable.

"Given the absolute value decline of MPLX units since the deal announcement in July, my recommendation is for this transaction to be voted down," he said in a press release.

Beginning Nov. 10, Marathon started upping its cash offer, first by $400 million and then another $205 million on Nov. 17. Initially, Marathon offered to pay $675 million in cash.

Nevertheless, after Marathon’s Nov. 17 offer, MarkWest unitholders stood to realize a 14% premium on their unit price. MarkWest unitholders were offered a 32% premium in July.

“We are pleased the overwhelming majority of MarkWest unitholders voting supported the combination and we look forward to delivering on the significant opportunities in front of the combined partnership,” said Gary R. Heminger, MPLX chairman and CEO. “This combination creates a large-cap diversified midstream partnership with an extraordinary growth profile, underpinned by MarkWest’s large organic growth backlog and MPC’s large inventory of MLP-eligible assets.”

Marathon has a portfolio of about $1.6 billion in MLP-eligible EBITDA it can drop down into MPLX. MPLX will also assume $4.2 billion in debt.

Frank Semple, MarkWest chairman, president and CEO, said the combined MLP will be strengthened by Marathon’s support.

“MPC’s significant pipeline and refinery operations will be critical for expanding and integrating MarkWest’s midstream platform throughout some of our nation’s most productive resource plays,” Semple said.

MarkWest is a leader in several natural gas shale plays including the Marcellus, Utica, Huron/Berea, Haynesville and Woodford, as well as the Granite Wash Formation.

MPLX, MarkWest and Marathon management will host an analyst and institutional investor meeting Dec. 3. The presentation will be webcast live beginning at 9 a.m. EST.

Contact the author, Darren Barbee, at dbarbee@hartenergy.com.