OMAHA, Nebraska (AP) — Billionaire Warren Buffett always tries to make sure that anyone who's willing to make a seven-figure donation just to have lunch with the investor gets their money's worth, so the meals often last more than three hours.

So far, so good.

"Nobody's asked for their money back," Buffett said.

The Berkshire Hathaway chairman and CEO said he hopes the annual lunch auction will again draw multimillion-dollar bids to benefit the Glide Foundation, which provides social services to the poor and homeless in San Francisco. But that's hard to predict, especially with more international interest — three of the past four winners came from outside the US.

"Some of these people I'd never heard of before they made the bid," Buffett said. This year's auction was to start yesterday evening with a $25,000 minimum bid on eBay, but the final price of the meal won't be set until the auction closes on Friday evening. The date of the lunch will be determined later, once the winner is known and agrees with Buffett on a time.

Last year, Canadian investment firm Salida Capital paid $1.68 million to dine with Buffett. And that price represented a discount over the record $2.11 million a Chinese investment fund manager paid in 2008, which was the most expensive charity item eBay had ever sold.

Buffett's investment success and folksy wisdom have earned him a devoted following. Last month, 37,000 people attended Berkshire's annual meeting in Omaha.

But apart from his popularity, Buffett thinks the work of Glide has also moved bidders to pay astronomical prices for the lunch in previous years.

"They may like the lunch, but they care about where the money's going, too," Buffett said. "I would, too, if I were in their position."

Buffett knows a bit about philanthropy. He is giving away the bulk of his fortune over time. The plan he launched in 2006 will eventually split most of his shares of Berkshire stock between five charitable foundations, with the largest chunk going to the Bill & Melinda Gates Foundation.

He has supported Glide ever since his late first wife, Susan, introduced him to Glide's founder, the Rev. Cecil Williams. Buffett said the organisation and Williams, who has led the non-profit for more than 45 years, do a remarkable job of helping people recover after they hit rock bottom.

"There's all kinds of people that need that kind of help, and I don't think anybody is better at providing it than Glide," he said.