(FORTUNE Magazine) –

A new wave of ship-jumping is underway. In early November, Oracle's CFO Greg Maffei quit just four months after leaving the same post at Microsoft. In October, Tenet Healthcare's CFO, Robert Shapard, left after seven months, and in August, Abercrombie & Fitch's president, Robert Singer, departed after 15. Isolated events? Richard Jacovitz at Liberium Research sees a trend. According to his data, executive turnover in the U.S. is heating up. Since January, when he started tracking 900 companies, turnover per month has more than doubled. Jacovitz blames Sarbanes-Oxley. "There's so much more pressure from both the board and outside shareholders," he says. "I really believe you're gonna see more of this."