More than $1 billion is now needed to make the cut on Forbes magazine's list of the 400 richest Americans. The minimum net worth for inclusion in this year's rankings was $1.3 billion, up $300 million from last year. As a result 82 US billionaires were excluded.

More than $1 billion is now needed to make the cut on Forbes magazine's list of the 400 richest Americans. The minimum net worth for inclusion in this year's rankings was $1.3 billion, up $300 million from last year. As a result 82 US billionaires were excluded. Collectively, the people who made the rankings are worth $1.54 trillion, compared with $1.25 trillion last year. The top of the list remained unchanged: Microsoft founder Bill Gates led the list for the 14th straight year with a net worth estimated at $59 billion. He was followed by Warren Buffett of Berkshire Hathaway in second place with an estimated $52 billion and casino mogul Sheldon Adelson, third with an estimated worth of $28 billion. Oracle's Larry Ellison maintained his ranking at four, with an estimated net worth of $26 billion. But the list showed some notable changes. Joining the top 10 of the country's richest for the first time were Google founders Sergey Brin and Larry Page, who tied for fifth place. The 34-year-old moguls' wealth has quadrupled since 2004 to an estimated $18.5 billion this year, while their company's stock value has surged 500 per cent. And, lower down, almost half of the 45 newcomers made their millions in hedge funds and private equity investments. The youngest member of this year's list was 33-year-old hedge fund manager John Arnold, who joined the ranks at 317 and a net worth of $1.5 billion. "Wall Street really led the charge this year," said Matthew Miller, editor of the Forbes list. "God only knows if they'll be on it next year. It really just depends on what the market does." Surging oil prices also helped some members of the list. Oil baron brothers Charles and David Koch also broke into the top 10, sharing the ninth spot with estimated wealth of $17 billion. Their promotion bumped the Walton family, heirs to the Wal-Mart Stores fortune, out of the top 10 for the first time since 1989. Climbing 19 places to seven was casino tycoon Kirk Kerkorian, who doubled his net worth to an estimated $18 billion. The 90-year-old investor is a majority shareholder in MGM Mirage — operator of the MGM Grand, Bellagio and other casinos — which saw record profits at several of its Las Vegas hotel-casinos. Rounding off the top 10 was Michael Dell of computer maker Dell, who was eighth with an estimated $17.2 billion. The magazine confirmed the worth of an individual's holdings in public companies by using the 31 August closing stock price, and estimated the value of private companies by evaluating comparable public firms in the industry. The list also takes into account philanthropic donations.