America's richest keep on getting richer The net worth of the richest Americans grew by 13 per cent in the past year to $1.7 trillion, Forbes magazine has said in its annual survey, and a familiar cast of characters once again populated the top of the magazine's annual list of the US uber-elite, including Bill Gates, Warren Buffett, Larry Ellison and the Koch brothers. The average net worth of the 400 wealthiest Americans rose to a record $4.2 billion, the magazine said. Collectively, this group's net worth is the equivalent of one-eighth of the US economy, which stood at $13.56bn in real terms according to the latest government data. However, the 13 per cent growth in the wealth of the richest far outpaced that of the economy overall, helping widen the chasm between rich and poor. Bill Gates, the chairman of Microsoft, topped the list for the 19th year in a row, with $66bn, up $7bn from a year earlier. Warren Buffett, chairman and chief executive of insurance conglomerate Berkshire Hathaway, stood second with $46bn, followed by Larry Ellison, head of software maker Oracle, with $41bn; and the Koch brothers, Charles and David, who run the energy and chemicals conglomerate that bears their name, Koch Industries, were tied for fourth with $31bn, Forbes said. The ranks of the top five were unchanged from a year earlier. Two notables dropped from the top 10. Casino magnate Sheldon Adelson - a prime backer of Mitt Romney - fell to 12 from No 8 last year, and financier George Soros dropped five places to 12. The disappointing stock market debut of Facebook also took a toll on the fortune of its founder and chief executive, Mark Zuckerberg. His net worth fell by nearly half to $9.4 bn, and he slid to 36th from No 14, Forbes said.