For the first time, the richest 400 tycoons in the US all have a personal wealth of at least $1bn (£526m), Forbes magazine has reported.
Microsoft boss Bill Gates kept top spot for a 13th consecutive year with investment guru-turned-philanthropist Warren Buffett in second place.
Casino and hotel owner Sheldon Adelson has leapt from 15th to third ranking.
The rich list as a whole is worth $1.25 trillion, compared with $1.13 trillion a year ago, Forbes said.
Four of the top 10 came from the Wal-Mart owning Walton family.
THE TOP FIVE
'$1m an hour'
Mr Adelson's surge in fortune comes largely from a decision to open a casino in Macau, a pennisula off south-eastern China renowned for its gambling.
Forbes estimates that Mr Adelson has been earning about $1m an hour for the past two years.
Two of the other biggest earners were the founders of search engine Google.
Apple Computers chief executive Steve Jobs was 49th on the list, with $4.9bn.
California is home to 90 of the 400 on the list, while another 44 live in New York.
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