Marathon Oil Corp. (NYSE: MRO) has appointed Lee Tillman as chairman of the U.S. shale producer, the Houston-based company said Jan. 30.

Tillman, president and CEO of Marathon, will succeed Dennis Reilley, effective Feb. 1. The company said in its release that Reilley had elected to retire after nearly six years as chairman and more than 17 years on the Marathon Oil board of directors.

“It’s been a privilege to work with Dennis. He has served our company and our shareholders with distinction, and has been a strong proponent in Marathon Oil’s transformational journey to a differentiated U.S. independent E&P,” Tillman said in a statement.

Tillman will continue to serve as Marathon’s president and CEO, a position he's held since 2013 when he joined the company after working with Exxon Mobil Corp. (NYSE: XOM) for over two decades.

Gregory Boyce, who was named Marathon’s lead independent director on Jan. 30, said in a statement: “Speaking on behalf of the board, we’re confident in Lee’s proven capabilities, leadership and vision for Marathon Oil. We’re pleased to announce him as our new chairman of the board.”

Boyce has been a director of the company since 2008. He will take on his new role on the Marathon Oil board effective Feb. 1.

Marathon’s multi-basin portfolio includes positions in the Bakken, Permian Basin, Stack/Scoop and Eagle Ford.

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