Early bids are in for a charity lunch with billionaire investor Warren Buffett.

By Monday afternoon the top bid was $40,100, but the auction is likely to fetch far more before it wraps up late Friday. Last year's winning bidder forked out more than $650,000 for lunch with Buffett and up to seven others at Manhattan steakhouse Smith & Wollensky.

Proceeds of the lunch with the 77-year-old Buffett, chairman of Berkshire Hathaway Inc, benefit the Glide Foundation, a nonprofit in San Francisco's Tenderloin district that offers programs for the poor, hungry and homeless. Buffett began donating the lunches in 2000.

The auction began Sunday on eBay Inc's website and ends Friday at 10 p.m. Last year's winner was Mohnish Pabrai, an Irvine, California-based investor who models his investment style on Buffett's.

The top bid on Monday appeared to have been made by an individual in San Luis Obispo, California. Bidders' identities are not revealed on the website. Only qualified bidders can take part in the auction, which started at $25,000.

The lunches have raised more than $2 million for Glide since going online in 2003. Previous auctions were held live, with winning bids of $25,000 to $32,000.

Buffett began donating the lunches after his wife Susan introduced him to the Rev. Cecil Williams, who founded Glide and runs the Glide Memorial United Methodist Church.

Buffett has pledged most of his fortune to the Bill & Melinda Gates Foundation and four family charities. He has said his Berkshire shares will go to philanthropy. Earlier this year Forbes magazine estimated Buffett's net worth at $62 billion, most of it invested in Berkshire.

Since taking over Berkshire in 1965, Buffett has transformed it from a failing textile maker into a sprawling insurance and investment company with more than 70 businesses.

Berkshire products include Geico car insurance, Dairy Queen ice cream and Fruit of the Loom underwear. Its investments include American Express Co, Coca-Cola Co and Wells Fargo & Co.