( CNN ) -- Fortune 's latest ranking of America 's 500 largest corporations includes more women CEOs than ever before . Women lead 18 of the 500 companies , including Hewlett-Packard ( 10th ) run by Meg Whitman and IBM ( 19th ) run by Ginni Rometty , both of whom started within the last year . Other executives to have shattered the glass ceiling include Patricia Woertz of agricultural processors Archer Daniels Midland ; Indra Nooyi who is CEO of Pepsico , Irene Rosenfeld who heads up Kraft Foods ; Ursula Burns who is CEO at Xerox and Sherilyn McCoy at Avon . Rometty is IBM 's first female CEO and Xerox chief Ursula Burns is the first African-American woman to head a Fortune 500 company . The top five female CEOs on the list all held positions in strategic planning before being appointed . There are an additional 21 female CEOs in the Fortune 501-1000 , some managing steel , oil and energy companies . Read more : 10 most powerful women in tech . Lists like the Fortune 500 typically generate debate about how to improve female representation in governance positions . Catalyst , a nonprofit research organization advocating for more women in business , found that in Canada women hold 14.5 % of board seats , a figure that rose by only half a percent between 2009 and 2011 . In America , women hold 16.1 % of board seats , an increase of less than half a percent from 2010 . About 10 % of the top 500 U.S. companies , and almost 40 % of Canada 's 500 largest companies have no women on their boards , according to Catalyst . In the UK , where only 9.8 % of FTSE250 companies are lead by women , and 44 % have no female board members at all , a report by former trade minister Lord Davies estimated that , at the current rate of change , it will take 70 years to achieve gender balance in the boardroom . Baroness Mary Goudie is founder of the 30 % Club , which encourages company chairs to commit to achieving at least 30 % women on UK corporate boards . She notes that , while there is a record number of women CEOs in the United States , `` on the other hand , you 've got hardly any women on boards . `` The United States does n't have the same regulatory situation as boards in the UK and parts of Europe . In the UK you can only do two terms on a board , so we 're seeing a turnaround for women , whereas in the States , people seem to get on a board and stay for a lifetime , almost . The pipeline is blocked forever . '' Despite this , Baroness Goudie feels female CEOs can influence the make-up of boards . `` They can try to influence the chairman of their company by saying , 'Look at the shortlist : How many women are you bringing on ? ' '' They may also indirectly benefit others aspiring to senior positions . `` A number of women CEOs have children . They are looking to make change and to encourage the pipeline . There 'll be a few who wo n't be helpful but the vast majority of women CEOs are doing all they can to encourage other women to go after these jobs . '' More from Leading Women : Want more female execs ? Sort out the household chores . Companies with fewer females in senior positions might be shooting themselves in the foot . Catalyst has also analyzed the performance of F500 companies with women board members . It found that , from 2004 to 2008 , the Fortune 500 companies with the most female board directors outperformed those with the least -- by 16 % on return on sales and by 26 % on return on invested capital . Companies which had three or more women on boards for at least four of those years outperformed those with the lowest rates of female representation by 84 % on return on sales , 60 % on return on invested capital and 46 % on return on equity .
This year 's Fortune 500 list includes the greatest number of female CEOs in history . Women helm some of America 's biggest 500 corporations . Campaigners say more women are still needed on boards .