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 US in 2006.
Microsoft founder Bill Gates tops the list for the 13th straight year, with a net worth of $53 billion US dollars.
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 Mr Gates and his wife.
It is estimated that Google founders Larry Page and Sergey Brin have made $3 million a day, each, over the past two years. Casino mogul Sheldon Adelson made $1 million an hour over the past two years.
Mr Adelson is this year's biggest gainer, leaping to third place, up from number 15 on last year's Forbes 400.
California contributes the most resident billionaires to this year's list with 90. New York City is home to 44.
