Pam Nicholson, president and chief executive of Enterprise Holdings, has landed at No. 17 on Fortune's list of the 51 Most Powerful Women in Business that also includes GM's Mary Barra, Facebook's Sheryl Sandberg, and Oprah Winfrey.

Nicholson runs the largest car rental company in the world, and also oversees Enterprise Fleet Management, which is now the second largest U.S. fleet management company behind Element Fleet Management. Brice Adamson, a senior vice president who runs the fleet management business, reports to Nicholson.

Nicholson has been a long-running fixture on this list, appearing for the first time in 2007.

The Enterprise car rental business maintains a global fleet of 2 million vehicles, which is more than twice the size of its next largest competitor. The company's brands include Enterprise, Alamo, and National Car Rental.

GM's chairman and CEO, Barra, appeared at No. 2 on the list behind Marillyn Hewson, Lockheed Martin's chairman, president, and CEO. Facebook's Sandberg, the company's chief operating officer, is No. 6. Kathryn Marinello, president and CEO of Hertz Global Holdings, appeared at No. 50.