The Fortune magazine announced its annual list of the 40 richest Americans under the age of 40 on Wednesday.

Topping the list is Michael Dell, 39, chairman and founder of Dell Computer. With a wealth of $17.95 billion, Dell has held the No. 1 spot since the list was started in 1999.

Larry Page and Sergey Brin of Google, both 31, hold the No. 4 and No. 5 spots with total wealth of $4.19 billion and $4.17 billion, more than four times their wealth last year when they first debuted on Fortune's '40 Under 40.'

Debuting this year, celebrities such as Britney Spears, Jennifer Lopez, Julia Roberts, and the Olsen twins, said a Fortune media release.

The list and related stories appear in the September 20 issue.

"How hard is it to stay on top?" asks Fortune. "For Michael Dell, not hard at all. But for the others, remaining at the peak is no mean feat."

The top ten on the '40 Under 40' list are:

• 1. Michael Dell, 39, CEO & Founder, Dell Computer ($17.95 billion)
• 2. Pierre Omidyar, 37, Chairman & Founder, eBay ($10.05 billion)
• 3. Jeff Skoll, 39, Chairman & Founder, Skoll Foundation ($4.69 billion)
• 4. Larry Page, 31, President, Products & Co-Founder, Google ($4.19 billion)
• 5. Sergey Brin, 31, President, Technology & Co-Founder, Google ($4.17 billion)
• 6. Jerry Yang, 35, Chief Yahoo & Co-Founder, Yahoo ($2.81 billion)
• 7. David Filo, 38, Chief Yahoo & Co-Founder, Yahoo ($2.57 billion)
• 8. Ken Griffin, 35, President & Founder, Citadel Investment Group ($1 billion)
• 9. Dan Snyder, 39, Chairman & Principal Owner, Washington Redskins ($823 million)
• 10. Marc Benioff, 39, Chairman & CEO, Salesforce.com ($376 million)

A number of people from previous lists have been dropped, some because they hit 40 (Amazon's Jeff Bezos, Gateway's Ted Waitt, Broadcomm's Henry Nicholas, RealNetwork's Rob Glaser, and basketball star Michael Jordan).

Others, such as Monte Zweben of Blue Martini, Scott Blum of Buy.com, and Vinny Smith of Quest Software are not on the list because their wealth no longer made the cut.

It remains to be seen whether Page and Brin of Google will have Dell-like staying power.

And though tech entrepreneurs still dominate the top ten, their numbers have dwindled by half since the list's inception in 1999. They have been replaced by entertainers such as Britney Spears, Jennifer Lopez, Julia Roberts, and the Olsen twins.

To compile the list, Fortune sorted through thousands of candidates, all younger than 40 as of the September 20 issue date.

Those who inherited their millions or earned most of their wealth outside the Untied States were excluded. Fortune then pored over proxies, insider-trading records, and other SEC documents. Thomson Financial helped to identify the richest and to research insider trades, said the release.

For celebrities and athletes, Fortune turned to industry reports in addition to interviewing attorneys, agents, and producers.

Final tallies include salaries and revenues from endorsements and box office sales, as well as the value of investments, exercisable options, and private-company holdings. Fortune adjusted for everything from taxes and assumed spending to agents' fees.