Bill Gates has one monopoly the government can't try to stop.

Microsoft's chairman topped Forbes magazine's rankings of the world's richest billionaires for the fourth straight year, as his net worth jumped 40 percent from a year ago to $51 billion.Forbes tightened the criteria for its rankings this year by including only the "working rich." Listed are billionaires who have built their own fortunes or are working with their inheritance rather than the silver-spoon set that is living off its wealth, Forbes said in its July 6 issue, released Sunday.

While fighting a government antitrust lawsuit against Microsoft, the world's largest software company, Gates easily fended off rivals to his billionaires' throne. The combined riches of five people - the heirs of Wal-Mart founder Sam Walton - still fell $3 billion short to rank No. 2 with $48 billion.

The wealthiest individual on the list behind Gates was investor Warren Buffett, No. 3 at $33 billion. Rounding out the top five were Microsoft co-founder Paul Allen at $21 billion and Canada's Kenneth Thom-son, head of publishing giant Thomson Corp., at $14.4 billion.

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 $4 billion, Forbes said.

The new criteria dropped several billionaires from the list, including the $15.3 billion Quandt family of Germany, a majority shareholder of BMW who ranked No. 10 last year; L'Oreal's founding Bettencourt family of France, worth $11.4 billion; and sisters Barbara Cox Anthony and Anne Cox Chambers, $7.1 billion heirs of the U.S. media company Cox Enterprises.

The 12th annual list, which excludes dictators and royalty, is a companion to Forbes' rankings of 400 richest Americans, which is slated for its Oct. 12 issue.

If royalty were included among the top billionaires, the Sultan of Brunei would have ranked third at $36 billion. The oil-rich sultan was richer than Gates until this year.

Suharto became eligible after quitting under pressure last month amid the economic crisis in Indonesia. 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.

Among business kingpins who made the list were media tycoon Rupert Murdoch at $5.3 billion; British entrepreneur Richard Branson at $1.9 billion; and Japanese real estate and transportation mogul Yoshiaki Tsutsumi, once the world's richest businessman, at $5.7 billion.

The average net worth of the top 200 billionaires was $4.7 billion, up from $3.9 billion in 1997.