David J. O’Reilly

With a degree in chemical engineering, David J. O'Reilly worked at Chevron Corporation for decades, starting as a process engineer, before being named chairman and CEO. Known for his informal, anti-hierarchical management style, he oversaw the successful merger of the company with Texaco, eventually making it the second largest oil company in the U.S. He also led the acquisition of Unocal Corporation, further expanding the company's oil and gas reserves. Updated 2009