Although women co-CEOs are not unusual among women-founded startups, female co-CEOs at large firms are even rarer than women running companies solo. We could not find any examples of two women sharing the CEO job at a Fortune 500 firm. And at Oracle, Safra Catz and the late Mark Hurd shared the co-CEO job for five years, from 2014 until 2019, when Hurd died from an undisclosed illness. (One caveat: This is based on data from Fortune’s yearly Fortune 500 rankings, which offer snapshots of corporate leadership at the time of publication. If other women were appointed to short-lived co-CEO roles between our publishing dates, we may have missed them.)