NEW YORK (Reuters) - Billionaire investor Warren Buffett is again the richest American, deposing Microsoft co-founder Bill Gates, after Forbes magazine recalculated the fortunes of some of the 400 wealthiest Americans.

Warren Buffett listens to a question during a news conference in Madrid, May 21, 2008. REUTERS/Andrea Comas

The magazine took another look at the fortunes of some of the billionaires on its Forbes 400 list to assess the effect of the worst financial crisis since the 1930s Depression and released a select list naming some of those hit hard.

But while 17 billionaires on Forbes list lost more than $1 billion in the past month, Buffett managed to boost his wealth by $8 billion to $58 billion, pushing him ahead of Gates, whose fortune fell to $55.5 billion from $57 billion.

Gates had been ranked No. 1 on the Forbes 400 list for the past 15 years with his Microsoft fortune.

Buffett made his money by building his company Berkshire Hathaway Inc into a $199 billion conglomerate that invests in undervalued companies with strong management. Late last month his company said it would invest $5 billion in Goldman Sachs Group Inc.

“We chose to focus on some of the more high-profile billionaires on The Forbes 400, and print a sampling of those who lost over $1 billion during the month of September,” said Forbes senior editor Matthew Miller.

The initial list, released on September 17, was calculated using publicly traded stock prices on August 29, while the revised fortunes of some billionaires uses October 1 prices.

Third place Oracle Corp founder Lawrence Ellison, saw his estimated $27 billion fortune drop to $25.4 billion, but he did not appear to lose his position.

When the list was released last month, four members of the Walton family, descendants of Wal-Mart Stores Inc founder Sam Walton, held positions 4 through 7, each with fortunes of about $23 billion.

New York City Mayor Michael Bloomberg was at No. 8 with a fortune estimated at $20 billion from his news and financial data empire, while brothers Charles and David Koch rounded out the top 10 with fortunes of $19 billion each from their manufacturing and energy company Koch Industries.

Forbes did not say whether any of those positions had changed.

Of the billionaires whose fortunes were revised by Forbes, casino magnate Sheldon Adelson was hit hardest by the economic turmoil with his fortune dropping $4 billion to $11 billion, and Charles Ergen, chairman of satellite broadcaster EchoStar, lost $2.2 billion and is now said to be worth $5.9 billion.

A list of some of the recalculated fortunes is availablehere.