China Petrochemical Corp., also known as Sinopec Group, and Houston-based Marathon Oil Corp. have chiefly relied on in-house counsel in a deal which will see the Chinese state-owned company acquire Marathon’s interest in an Angolan offshore oil and gas field for $1.52 billion.

Sinopec’s acquisition of Marathan’s 10 percent stake will increase the Chinese company’s interest in the field to 15 percent. Two years ago, Sinopec bought a five percent stake in the same block from French oil and gas company Total S.A. for $983 million.

The deal is pending approval from the governments of China and Angola.

According to spokespersons at both companies, legal work on the transaction was handled primarily by in-house teams led by Sinopec general counsel Zhang Jixing and Marathon general counsel Sylvia Kerrigan.

Sinopec has made several energy overseas acquisitions. Last year, Vinson & Elkins advised the company on a separate $2.5 billion deal with Total to acquire a 20 percent stake in a Nigerian offshore block. Also in 2012, the firm now known as Herbert Smith Freehills advised Sinopec on its $1.5 billion acquisition of a 49-percent equity interest in Talisman Energy, the U.K. North Sea division of Canadian oil and gas company Talisman Energy Inc.