For the first time, everyone on this year's Forbes rich list is a billionaire. The magazine's annual ranking of America's 400 wealthiest individuals found the collective net worth of those listed reached a record-breaking $1.25 trillion in 2006.
Microsoft founder Bill Gates tops the list for the 13th straight year, with a net worth of $53 billion.
He is followed by US philanthropist Warren Buffett - who made headlines this year by bequeathing the bulk of his fortune to the charitable foundation run by Gates and his wife, Melinda.
Casino mogul Sheldon Adelson made $1m an hour over the past two years. Adelson is this year's biggest gainer, leaping to third place, up from number 15 on last year's Forbes 400.
Fourth richest on the list was Larry Ellison, founder of business software giant Oracle with a net worth of $19.5 billion, followed by Paul Allen ($16 billion).
Five members of the Walton family, the heir to the Wal-Mart fortune, were among the top 11 on the list. Jim Walton was the wealthiest at number six on the list with $15.7 billion, followed by his sister Christy ($15.6 billion) and brother S Robson Walton ($15.6 billion).
Another Walton sibling, Alice Walton, was tied for ninth wealthiest ($15.5 billion), and the matron of the family, Helen Walton, was ranked 11th ($15.3 billion).
Personal computer mogul Michael Dell was tied for ninth on the list with an estimated worth of $15.5 billion. Google's co-founders Sergey Brin and Larry Page were also prominent on the list. Brin was number 12 with $14.1 billion and Page right behind with $14 billion, Forbes said.
According to the US Department of Labor's Bureau of Labor Statistics, the median income of the nation's 105.9 million full-time wage and salary workers is $34,268 a year.
