The collective net worth of the wealthiest Americans increased by $120 billion over the past year to $1.25 trillion.

Bill Gates, founder of Microsoft, kept his top spot on the Forbes list for the 13th straight year as his fortune grew to $53bn.

Number two on the list was Warren Buffett, the famous investor, who announced plans this year to give away 85 per cent of his fortune. He saw his net worth increase to $46bn, Forbes said.

The top climber on the list was Sheldon Adelson, a self-made Las Vegas casino mogul who joined the top 10, listed third on the list with a net worth of $20.5bn.

Fourth richest on the list was Larry Ellison, founder of  business software giant Oracle with a net worth of $19.5bn.

Five members of the Walton family, the heir to the Wal-Mart supermarket fortune, were among the top 11 on the list. Jim Walton was the wealthiest at number six on the list with $15.7bn, followed by his sister Christy with $15.6bn and brother S Robson Walton with $15.6bn.

Google's co-founders, Sergey Brin and Larry Page, were also  prominent on the list. Brin was number 12 with $14.1bn and Page was next in line $14bn, Forbes said. Both men are the youngest on the list at 33 years old.

 

More than one in five billionaires came from the western US state of California, and about one in seven came from New York.

 

In contrast, the US Department of Labour's Bureau of Labour Statistics says that the median income of the nation's 105.9 million full-time wage and salary workers is $34,268 per year.