Marathon Oil Corp. plans to sell most of its aging offshore assets in the Gulf of Mexico for $205 million.

The Houston-based oil producer has reached a deal to sell properties it operates in the greater Ewing Bank area as well as non-operated producing interests in the Petronius and Neptune fields.

The deal is expected to close before the end of the year. Marathon did not disclose the buyer.

The assets represent “a majority” of Marathon’s producing properties in the Gulf, the company said.

The move will allow the company to put more attention on its shale drilling projects.

“As the success of our U.S. resource (shale) plays has continued to raise the bar for capital allocation, it has become increasingly difficult for new conventional exploration opportunities to compete from a cost, quality and risk perspective,” Mitch Little, Marathon’s vice president of international and offshore exploration and production operations, told analysts in an earnings call last week.

Under the deal, Marathon will retain its interests in some producing assets and acreage in the Gulf as well as its stake in the Gunflint development, where it holds an 18 percent non-operated working interest, and Shenandoah discovery, where it has holds a 10 percent interest.