(Updates share price in last paragraph.)

Dec. 10 (Bloomberg) -- Marathon Oil Corp. said Chief Operating Officer David E. Roberts Jr., once viewed as a possible successor to Chief Executive Officer Clarence Cazalot, is resigning to pursue other interests.

The resignation will be effective Dec. 14, Houston-based Marathon said in a statement today. Lee Warren, a company spokeswoman, declined to give his age or specify why Roberts is leaving the company.

Roberts joined Marathon in 2006 as the senior vice president for business development and became the executive vice president of upstream, which includes exploration and production, in 2008. He was named COO when the company spun off its refining operations last year and Cazalot, 62, became chairman and CEO.

“I’m surprised,” said Philip Weiss, an analyst at Argus Research in New York who rates the shares at hold and owns none. “I think of him as being highly regarded, as being a good solid number two.”

Marathon fell 1.8 percent to $30.36 at the close in New York. The shares, which have 16 buy and seven hold ratings from analysts, have climbed 3.7 percent this year.

--Editors: Tina Davis, Jessica Resnick-Ault

To contact the reporter on this story: David Wethe in Houston at dwethe@bloomberg.net

To contact the editor responsible for this story: Tina Davis at tinadavis@bloomberg.net