WASHINGTON (AP) -- Exxon Mobil's $60 billion deal to buy Pioneer Natural Resources on Thursday received clearance from the Federal Trade Commission, but the former CEO of Pioneer was barred from joining the new company's board of directors.

The FTC said Thursday that Scott Sheffield, who founded Pioneer in 1997, colluded with OPEC and OPEC+ to potentially raise crude oil prices. Sheffield retired from the company in 2016, but he returned as president and CEO in 2019, served as CEO from 2021 to 2023, and continues to serve on the board. Since Jan. 1, he has served as special adviser to the company's chief executive.

"Through public statements, text messages, in-person meetings, WhatsApp conversations and other communications while at Pioneer, Sheffield sought to align oil production across the Permian Basin in West Texas and New Mexico with OPEC+," according to the FTC. It proposed a consent order that Exxon won't appoint any Pioneer employee, with a few exceptions, to its board.

Dallas-based Pioneer said in a statement it disagreed with the allegations but would not impede closing of the merger, which was announced in October 2023.

"Sheffield and Pioneer believe that the FTC's complaint reflects a fundamental misunderstanding of the U.S. and global oil markets and misreads the nature and intent of Mr. Sheffield's actions," the company said.

The deal with Pioneer vastly expands Exxon's presence in the Permian Basin, a huge oilfield that straddles the border between Texas and New Mexico. Pioneer's more than 850,000 net acres in the Midland Basin will be combined with Exxon's 570,000 net acres in the Delaware and Midland Basin, nearly contiguous fields that will allow the combined company to trim costs.