US philanthropists had a "blockbuster" year in 2006, with the 60 most generous Americans giving $50.5 billion (€38.4bn) dwarfing the $4.3 billion donated in 2005. Topping a list compiled by the Chronicle of Philanthropy was Warren Buffett, the investment guru, who in June pledged $43.5 billion of his fortune to charity, mainly to the Bill & Melinda Gates Foundation, created by the founder of Microsoft.

Even without Mr Buffett's pledge, the other 59 donors gave $7 billion, up from $4.3 billion in 2005.

Excluding Mr Buffett's donation, the median amount that donors on the list committed in 2006 was $60 million, compared with $32.5 million in 2005.

The number of gifts of at least $100 million also increased, from 11 in 2005 to 21.

Donors broadened the scope of interests to include global warming, microfinance initiatives, stem-cell research and the advancement of human rights for gay people, according to Stacy Palmer, editor of the Chronicle, a trade newspaper.

"Younger donors and a new generation of donors are interested in different causes. It used to be colleges and hospitals that dominated, but we are seeing a lot of interest in other causes now," Ms Palmer said.

The source of philanthropic dollars has also shifted from the east coast, with nearly half the US's top 10 donors last year based on the west coast.