Buffett, who made much of his money investing in and buying insurance companies, saw his wealth rise mainly because of the increasing value of stock in his company, Berkshire Hathaway.
He announced in 2006 that he was giving most of his money to Bill Gates's charity, the Bill and Melinda Gates Foundation, after he dies.
Gates's Microsoft was recently fined a record $1.4bn by the European Commission for anti-competitive behaviour.
The commission said the US software company had defied its 2004 order to provide information so that rival programmes worked better with Microsoft products and had instead charged high royalties for the details.