He has topped Forbes magazine's rankings of the world's richest billionaires for the fourth straight year.

The software boss easily fended off rivals to his billionaires' throne.

To cap it all, his net worth has jumped 40% from a year ago to $51bn (£30.5bn).

Americans lead the list, with 12 entries in the top 20. They include the Walton family, who own Wal-Mart Stores ($29bn), Michael Dell, boss of the Dell Computer Corp ($6.1bn) and the Haas family, which runs jeans giant Levi Strauss ($5bn).

Britons lag behind in the money stakes. Not one makes the top 100.

Forbes tightened the criteria for its rankings this year by including only the "working rich".

Listed are billionaires who have built their own fortune or are working with their inheritance rather than the silver-spoon set that is living off its wealth. It excludes dictators and royalty.

If royalty were included among the top billionaires, the oil-rich Sultan of Brunei would have ranked third at $36bn.

One notable new member of this year's list was the family of former Indonesian President Suharto, whose 32 years in power enabled him to amass stakes in about 3,200 Indonesian companies and a family fortune of about $4bn.

Asia's financial retreat reduced its representation among the top 200 billionaires to 44 from 56 last year.

American billionaires on the list rose to 70 from 60, while Europeans accounted for 52, up from 44.

Merchant banker Bruno Schroder is the first British entry in the new rankings, in joint 111th place, worth $1.7bn.

He was followed by entrepreneur Richard Branson in 173rd position, whose fortune is estimated at $1.6Bn.

The rich list top 10

• 1: Bill Gates, US, $51bn, Microsoft Corporation
• 2: Walton family, US, $48bn, Wal-Mart Stores
• 3: Warren Buffett, US, $33bn, Berkshire Hathaway
• 4: Paul Gardner Allen, US, $21bn, Microsoft Corporation
• 5: Kenneth Thomson, Canada, $14.4bn, Thomson Corporation
• 6: Forrest Edward Mars Sr and family, US, $13.5, Inheritance
• 6: Jay A and Robert A Pritzker, US, $13.5, Financiers
• 8: Prince Al Waleed Bin Talal Al Saud, Saudi Arabia, $13.3bn, investments, construction, banking
• 9: Lee Shau Kee, Hong Kong, $12.7bn, real estate
• 10: Theo and Karl Albrecht and family, Germany, $11.7, retailing