Forty wealthy families and individuals have joined a campaign to give at least half their wealth to charity, according to a list released Wednesday.

Billionaire investor Warren Buffett released the list six weeks after he and Microsoft Corp. co-founder Bill Gates launched a drive to get other billionaires to donate most of their fortunes.

Warren Buffett waves to Berkshire Hathaway shareholders in May 2009. In 2006, Buffett decided to give 99 per cent of his fortune to charity. (Nati Harnik/Associated Press)

"We're off to a terrific start," Buffett said.

Buffett, the CEO of Berkshire Hathaway, decided in 2006 to give 99 per cent of his fortune to charity.

At the time he was worth about $44 billion US. After five years of investment returns while making annual gifts to five foundations, Buffett's fortune now totals nearly $46 billion.

The pledges follow 70 to 80 calls Buffett, Bill and Melinda Gates, and a few others made to some of the wealthiest individuals in the United States.

Among those who have pledged are Montreal-born Jeff Skoll, the founding president of eBay, New York Mayor Michael Bloomberg, filmmaker George Lucas, media mogul Ted Turner and Microsoft co-founder Paul Allen.

Among those who haven't signed the pledge, some prefer to keep their philanthropy anonymous, some were not available to talk and others were not interested, Buffett said.

Buffett said he and Bill Gates also will meet with groups of wealthy people in China and India within the next six months to talk about philanthropy.

They hope the idea of generosity will spread, but they have no plans to lead a global campaign, Buffett said.

Gates and Buffett estimate their efforts could generate $600 billion dollars in charitable giving. In 2009, American philanthropies received a total of about $300 billion in donations, according to The Chronicle of Philanthropy.

With files from The Associated Press