"Mr Buffett is one of the market's most respected and successful long- term investors. We are delighted with the vote of confidence in American Express that the Berkshire Hathaway share purchases represent," American Express enthused yesterday.
Mr Buffett's spokesperson in Omaha, Nebraska, was unwilling to supply any further information about the purchase or Berkshire Hathaway or Mr Buffett's intentions
Yesterday's statement by American Express confirmed that Berkshire Hathaway had built its stake by converting $300m worth of preferred stock acquired in 1991 into 14 million American Express shares in August last year.
By the end of the year the stake had risen to 27.7 million shares, and further purchases this year had increased the holding to 48.5 million by Monday evening.
American Express is in a growth phase, and the company recently reported record earnings and revenue growth in calendar 1994.
Mr Buffett is not thought to have asked for a seat on the board but it seems likely he will be asked to join shortly.
Berkshire Hathaway's investments include stakes in Coca-Cola, Gillette, the Washington Post and other media groups, and Salomon Inc the New York investment house.
Mr Buffett is the author of a recent book on investment policy which is highly critical of short-term investment policy and contemporary investment theories. He is a long-term investor with a relatively a conservative investment policy.
"The problem with over-diversification is if you have a harem of 40 women you never get to know any of them very well," he is once supposed to have said. But his personal wealth was estimated recently by Forbes Magazine at $9.2bn, second only to Bill Gates of Microsoft in the list of the 400 richest Americans.