America's 400 wealthiest citizens lost an estimated $74bn this year due to the economic slowdown and weak equity markets, according to the latest survey by Forbes magazine. That is equivalent to the gross domestic product of Egypt, which has a population of more than 63m. Collectively, America's wealthiest 400 citizens are worth a massive $872bn, nearly double the GDP of Australia. Microsoft chief Bill Gates still tops the list, but his mountain of cash dwindled by more than $15bn this year, making him worth $43bn. At this rate of decline he might find himself knocked off the number one spot by America's savviest investor Warren Buffett. The Sage of Omaha, as he is known to millions of American investors, added $3.7bn to his personal fortune of $36bn this year, despite the carnage in world equity markets. Third place on this list is held by Paul Allen, another Microsoft co-founder, whose net worth is estimated at $21bn, down from $30.4bn the year before. The next five places are occupied by members of the Walton family, owners of the world's biggest retailer, Wal-Mart. Larry Ellison, founder of Oracle, whose personal fortune dwindled from $26bn last year to $15.2bn, occupies ninth place, down from fourth the year before. Rounding out the top ten was Microsoft chief executive Steven Ballmer with a net worth of $11.9bn, down from $16.6bn.