Company: Sunoco
Fortune 500 rank: 68
First year as CEO: 2010
Most Powerful Women rank: 35
The only female head of Big Oil in the U.S., Elsenhans has made bold moves to overhaul the $37 billion refiner. She's sold the chemicals business and ditched three money-losing refineries. She is relying more on retail fuels and logistics, with high returns and stable cash flows.
NEXT: Ursula Burns