In July Reed took over the Fortune 500 energy services company with $9 billion in 2010 revenue. The industry veteran once served as president and CEO of Sempraís San Diego Gas
& Electric and Southern California Gas. She also sits on the Halliburton board.
The list is compiled by FORTUNE editors, who consider four criteria: the size and importance of the womanís business in the global economy, the health and direction of the
business, the arc of the womanís career (resume and runway ahead), and societal and cultural influence.