Patty Stonesifer, former CEO of the Bill & Melinda Gates Foundation, told The Associated Press on Wednesday that Gates and Buffett have been campaigning for the past year to get others to donate the bulk of their wealth.
The friends and philanthropic colleagues are asking people to pledge to donate either during their lifetime or at the time of their death.
The handful of billionaires approached so far have embraced the campaign, said Stonesifer, a close friend of Gates who offered to speak about the effort. Four wealthy couples have already announced their pledges, including Los Angeles philanthropists Eli and Edythe Broad, Gerry and Marguerite Lenfest of Philadelphia, John and Ann Doerr of Menlo Park, California, and John and Tasha Mortgridge of San Jose, California.
Gates and Buffett are calling their campaign The Giving Pledge. Buffett, chairman and CEO of Berkshire Hathaway Inc., said in a letter introducing the concept that he couldn't be happier with his decision in 2006 to give 99 percent of his roughly $46 billion fortune to charity.
Besides Buffett's pledge to the foundation, he also plans to give Class B Berkshire shares to the Susan Thompson Buffett Foundation, which he and his late first wife started, and the three foundations run by his three children.
Buffett said in 2006 that his other 73,332 Class A shares of Berkshire stock, worth about $8 billion, would also go to philanthropy, but he didn't spell out how those shares would be distributed.
Gates and Buffett are asking each individual or couple who make a pledge to do so publicly, with a letter explaining their decision.
"The pledge is a moral commitment to give, not a legal contract. It does not involve pooling money or supporting a particular set of causes or organizations," they explain in a written statement about the project.
AP Business Writer Josh Funk in Omaha contributed to this report.