The top of the list of US billionaires is still dominated by dynastic wealth, according to the latest annual survey by Forbes magazine, while 272 of the 400 richest Americans are self-made.
Bill Gates, the founder of Microsoft, tops the list once again with a fortune of $54bn, but six of the Top 10 are heirs to company founders from the past.
This distribution of wealth is being highlighted in a campaign by Mr Gates and his friend Warren Buffett, who is No 2 on the list, to urge billionaires to give at least half of their fortunes to charity before they die, instead of handing them to their children.
And Mr Buffett even tells the latest issue of Forbes that he uses their annual Forbes 400 list as a recruiting tool for his Giving Pledge, to which 40 members of the elite billionaires' club have signed up.
"The way I got the message out was to look down that 400 list and start making phone calls," Mr Buffett said. "Bill and Melinda [Gates] did the same thing. So keep publishing the list so I can milk it."
The rebound by the economy and by financial markets has helped to swell the fortunes of the richest 400 Americans, among whom the total wealth has risen to $1.37 trillion, up 8 per cent in a year. In 2009, the price of admission to the list fell below $1bn for the first time since 2006, but it rose back into 10 figures this year.
New entrants include two with ties to Facebook, co-founder Eduardo Saverin, who is worth $1.15bn, and Mark Zuckerberg's Harvard University room-mate, Dustin Moskovitz. Mr Moskovitz left Facebook in 2008 but still has a stake in the social networking giant that is worth $1.4bn on the private market where the company's shares trade. At 26, eight days younger than Mr Zuckerberg, Mr Moskovitz is now the youngest billionaire on the list.
Mr Zuckerberg, meanwhile, enjoyed the biggest percentage increase in his fortune of anyone on the list, more than tripling to $6.9bn. Now No 35 on the list, he has leapfrogged the established media and technology moguls Rupert Murdoch and Steve Jobs, who are worth $6.2bn and $6.1bn respectively.
Some of the biggest losers in the past 12 months have been clobbered by declining share prices in their companies. Stephen Schwarzman, founder of the private equity group Blackstone, lost $600m from a net worth of $4.7bn a year ago. The mobile phone entrepreneur Craig McCaw, founder of Clearwire, dropped off the list, despite having been worth $1.65bn last year.
The heirs to the retail magnate Sam Walton, founder of Wal-Mart, and of Fred Koch, founder of the industrial conglomerate Koch Industries, dominate the top of the list once again this year. David Koch, jointly at No 5 with his brother Charles, joked about his wealth on giving a gift to his former university in 2003: "One day, my father gave me an apple. I soon sold it for five dollars and bought two apples and sold them for ten. Then I bought four apples and sold them for twenty. Well, this went on day after day, year after year, until my father died and left me $300m."
Forbes magazine asked the 400 billionaires for their favourite pastimes, and the top five were: education (73), art (64), sports (56), science (31) and the Giving Pledge (28).
Forbes Rich List: Top 25
1 Bill Gates, 54, Microsoft, $54bn
2 Warren Buffett, 80, Berkshire Hathaway, $45bn
3 Larry Ellison, 66, Oracle, $27bn
4 Christy Walton, 55, Walmart, $24bn
5= Charles Koch, 74, KS manufacturing, energy, $21.5bn
5= David Koch, 70, manufacturing, energy, $21.5bn
7 Jim Walton, 62, Walmart, $20.1bn
8 Alice Walton, 61, Walmart, $20bn
9 S. Robson Walton, 66, Walmart, $19.7bn
10 Michael Bloomberg, 68, Bloomberg, $18bn
11= Larry Page, 37, Google, $15bn
11= Sergey Brin, 37, Google, $15bn
13 Sheldon Adelson, 77, casinos, hotels, $14.7bn
14 George Soros, 80, hedge funds, $14.2bn
15 Michael Dell, 45, Dell, $14bn
16 Steve Ballmer, 54, Microsoft, $13.1bn
17 Paul Allen, 57, Microsoft, investments, $12.7bn
18 Jeff Bezos, 46, Amazon, $12.6bn
19 Anne Cox Chambers, 90, GA Cox Enterprises, $12.5bn
20 John Paulson, 54, hedge funds, $12.4bn
21 Donald Bren, 78, real estate, $12bn
22 Abigail Johnson, 48, Fidelity, $11.3bn
23 Phil Knight, 72, Nike, $11.1bn
24= Carl Icahn, 74, leveraged buyouts, $11bn
24= Ron Perelman, 67, leveraged buyouts, $11bn