U.S. billionaires pledge fortunes to charity

A total of 40 of the richest people in the United States, including Microsoft founder Gates and investor Buffett, now have taken the pledge.

Since launching the campaign in June, Buffett, Gates and his wife Melinda have spoken to about 20 percent of the wealthiest people in the United States -- 70 to 80 billionaires -- in a bid to persuade them to give away their fortunes.

Gates has an estimated $53 billion fortune, which places him second on the Forbes magazine list of the world's richest people, and Buffett, who made his fortune with insurance and investment company Berkshire Hathaway Inc, ranks third on the list with $47 billion.

Forbes said the United States is home to 403 billionaires, the most of any country. Individual Americans gave more than $227 billion in 2009, according to the Giving USA report by the Center on Philanthropy at Indiana University, down just 0.4 percent from the previous year despite the U.S. recession.