More than three dozen billionaires, including well-known philanthropist ( 慈善家 ) David Rockefeller, have promised at least half of their fortunes to charity, joining a programme that Bill and Melinda Gates and Warren Buffett started in June to encourage other wealthy people to give. The pledge is currently worth about $ 150 billion, but the programme predicts it will ually be worth $ 600 billion. "During even the Depression's worst years, my parents gave money - about 8% of their annual income of $ 2200," said Lorry Lokey, one of the donors, on the website of the programme, the Giving Pledge, "I remember saying to my mother that we can't afford that. But she said we have to share with others." The pledge has been a matter of some debate in philanthropic and non-profit circles, with some experts dismissing it as mere publicity and others predicting that it would produce a flood of new money to support non-profit groups. Buffett said the real value of the pledge was found in the example it set and in the sentiments ( 情感 ) expressed in the letters posted on the website. Buffett and Gates will hold several dinners later this year to recruit more billionaires, and members of the Giving Pledge will meet annually to discuss their philanthropy. The pair are due to meet some wealthiest people in China next month and India in March. "We hope this catches fire in some other countries," Buffett said, "If they want to take what we think is a good idea and run with it, we will be cheering." Buffett said the number of people who had agreed to sign on was at the high end of his expectations. He said some people who declined to sign the pledge were planning to give away most of their wealth but did not want to draw attention to those plans. Energy tycoon ( 大亨 ) Pickens, who is worth about $ 1 billion, said in his Giving Pledge letter: "I've long stated that I enjoy money, and I enjoy giving it away. I'm not a big fan of inherited wealth. It generally does more harm than good."