The stalled U.S. economy does not appear to be taking a toll on the richest Americans, who saw their combined wealth rise 12 percent over the past year.

U.S. business magazine Forbes released its annual list of the 400 wealthiest Americans Wednesday, with Microsoft founder Bill Gates leading the way for the 18th straight year.

Gates is worth an estimated $59 billion, putting him easily ahead of investor Warren Buffett, who placed second with a net worth of $39 billion, despite losing $6 billion over the past year.

Forbes says more than half of Buffett's loss came as a result of giving money to charity.

Other notable names in the top 10 are Oracle founder Larry Ellison, worth $33 billion, Wal-Mart heirs Christy Walton, Jim Walton and Alice Walton, all worth more than $20 billion. Investor George Soros and casino owner Sandy Adelson also made the top 10, along with industrialists Charles and David Koch.

The biggest gainer from last year's list is Facebook founder Mark Zuckerburg, who saw his fortune increase by $10.6 billion, ranking him 14th. Google's Sergey Brin and Larry Page are tied at 15th overall, each adding almost $2 billion to their personal fortunes.

Forbes says the 400 richest Americans have a combined wealth of $1.53 trillion, almost as much as the total economic output of Canada.

The magazine also says 70 percent of the Americans on this year's list are self-made billionaires, up from 55 percent in 1997.