(Fortune) -- Susan Ivey, Chairman and CEO of R.J. Reynolds Tobacco (Charts), ranks No. 20 on Fortune's 2006 list of 50 Most Powerful Women.

Since she was named chairman in January, Ivey has watched Reynolds American's stock price climb 33%. But litigation risk could dampen the blaze at the $8.3 billion tobacco company, maker of a third of all cigarettes sold in the U.S.

By the key criteria Fortune uses in assembling its annual list - the size, importance, and health of each business in the global economy, and the momentum of each woman's career (along with her social and cultural influence) - there's no question that the power of women in the corporate sphere is rising.

Indeed, it could be called the year of the Most Powerful Woman CEO. The top seven positions on Fortune's 2006 Most Powerful Women list are held by CEOs.

Some other pwerful women on the list include: Anne Sweeney, Disney Media Networks (Charts); Sallie Krawcheck, Citigroup (Charts); Susan Arnold, Procter & Gamble (Charts); Ellen Kullman, DuPont; (Charts) Mary Minnick, Coca-Cola (Charts); Linda Dillman, Wal-Mart (Charts); and Charlene Begley, General Electric (Charts).

Next: Full list: 50 Most Powerful Women at http://money.cnn.com/popups/2006/fortune/mostpowerfulwomen/1.html

Plus: Most Powerful Women: 10 Highest-Paid at http://money.cnn.com/popups/2006/fortune/womenpay/index.html