Aon has told analysts it expects to reduce its tax rate, which averaged 28% over the past five years, by five percentage points over time, which could boost profits by about $100 million annually.

Since 2009, at least 10 U.S. public companies have moved their incorporation address abroad or announced plans to do so, including six in the last year or so, according to a Wall Street Journal analysis of company filings and statements. That’s up from just a handful from 2004 through 2008…

U.S. multinationals often pay far less than 35% because of various breaks, including the option of deferring the payment of U.S. taxes on foreign earnings until they are brought to the U.S. Those companies could pay higher taxes under Obama administration proposals to limit the benefits of deferral. Rowan cited that potential change in announcing its move.

Obama administration officials play down the significance of the recent company moves and say their proposals would encourage companies to stay in the U.S.