(FORTUNE Magazine) – And the young captains of industry thought last year was bad. This year the average worth of those on FORTUNE's fourth annual list of the 40 richest self-made Americans under 40 (excluding perennial No. 1 Michael Dell, who is so much richer than everyone else that he skews the numbers) has plunged to $415 million, down from a high of $1.45 billion in 2000 (see the chart on the back page of the foldout).

Now that most boom-time dot-commers are too poor to make the list, who's left? Well, there are those lucky ones whose companies appear to have weathered the storm, such as eBay's Pierre Omidyar (No. 2) and Amazon.com's Jeff Bezos (No. 4). There are those who cashed out their stock or sold their companies before the market tanked, such as former Yahoo COO Jeff Mallett (No. 28) and Inktomi co-founder Paul Gauthier (No. 31)--people who in many cases are now incurring the wrath of shareholders. And, of course, there are the celebrities, such as hoopster Shaquille O'Neal (No. 22) and actress Julia Roberts (No. 26), whose astronomical asking prices have held up through the downturn. (For more on the 40 under 40, go to www.fortune.com/40.)

To put the list together, we sorted through thousands of candidates--all younger than 40 as of our Sept. 16 issue date--who have built their own fortunes in the U.S. (For a sampling of rich under-40s who have inherited their wealth or earned it overseas, see the back page of the foldout.) When calculating the wealth of those with holdings in public companies, we relied on proxy statements, insider-trading records, and various public documents; we included the value of exercisable options.

Gauging the wealth of those who own private companies was more complicated. We relied on estimates from investment bank Houlihan Lokey Howard & Zukin; Kagan World Media and Revolution Partners provided additional assistance. If we couldn't verify candidates' private holdings to our satisfaction, we eliminated them. For example, Larry Page and Sergey Brin, co-founders of search engine Google, may well have qualified--but they would not divulge their ownership stakes.

Celebrities provided different challenges. To estimate their earnings, we consulted entertainment attorneys, agents, music producers, and other insiders. Burns Sports & Celebrities provided estimates of athletes' endorsement deals, and Soundscan gave us estimates of record sales. We factored in salaries, private-company holdings, endorsements, and box-office sales, minus taxes and agents' fees, and assumed reasonable spending and investment levels.

Before you turn the page, we'd like to call your attention to some particularly interesting newcomers. Two people on the list--Elon Musk (No. 23), founder of online-payment middleman Paypal, and Jeffrey Zients (No. 25), founder of health-care consulting firm Advisory Board Co.--were catapulted there for the first time after their companies conducted successful IPOs. IPOs? This year? Maybe youthful entrepreneurship isn't dead after all. --Julia Boorstin, Jonah Freedman, and Christopher Tkaczyk

1 Michael Dell Chairman/CEO Dell Computer WEALTH $16.30 billion - AGE 36 Though Dell stock has fallen 15% since last year, Dell's wealth is up thanks to big gains in his private investment fund. LAST YEAR'S RANK: No. 1, with $17.08 billion

2 Pierr Omidyar Chairman/Founder eBay WEALTH $4.39 billion - AGE 34 "If I had [had] a blank check from a VC... things might have gone much worse," he said recently of eBay's early days. LAST YEAR'S RANK: No. 6, with $3.44 billion

3 Jeff Skoll Vice President eBay WEALTH $2.63 billion - AGE 36 This former eBay VP left the company last year to focus on his foundation, which funds community charities. LAST YEAR'S RANK: No. 8, with $2.16 billion

4 Jeff Bezos Chairman/President/CEO Amazon.com WEALTH $1.66 billion - AGE 38 With his stock up 13.5% since last year (Amazon recently showed its first pro forma profit), Bezos's wealth has risen more than anyone else's on the list. LAST YEAR'S RANK No. 5, with $1.23 billion

5 Ted Waitt Chairman/CEO/Co-Founder Gateway WEALTH $1.05 billion - AGE 39 He made more than $1 billion before taxes by selling Gateway stock over the past few years, but Waitt still owns nearly a third of the big PC maker. LAST YEAR'S RANK No. 4, with $1.87 billion

6 Dan Snyder Chairman/Principal Owner Washington Redskins WEALTH $664 million - AGE 37 Attention, cash-strapped baseball teams: Snyder is part of a campaign to lure a major-league ball club to Washington, D.C. LAST YEAR'S RANK No. 10, with $604 million

7 David Filo Chief Yahoo/Co-Founder Yahoo WEALTH $551 million - AGE 36 The man still won't sell! Co-founder Filo, who owns 8% of the company, has ridden Yahoo stock down from a high of $238 to a recent $12. LAST YEAR'S RANK No. 7, with $730 million

8 Jerry Yang Chief Yahoo/Co-Founder Yahoo WEALTH $514 million - AGE 33 Yang has filed to sell three million Yahoo shares next year--more than he's ever unloaded in the six years since the company's IPO. LAST YEAR'S RANK No. 8, with $721 million

9 Michael Jordan Basketball Player Washington Wizards WEALTH $408 million - AGE 39 His Airness calls wife Juanita--who filed for divorce last fall but changed her mind a month later--"the chief of finances in our household." LAST YEAR'S RANK No. 13, with $398 million

10 Vinny Smith Chairman/CEO Quest Software WEALTH $398 million - AGE 38 The tech-spending slowdown hammered Quest's stock price so hard that Smith's net worth has fallen nearly 80% over the past two years. LAST YEAR'S RANK No. 6, with $780 million

11 Percy Miller (Master P) CEO No Limit WEALTH $293.8 million - AGE 33 The longtime rap mogul says he's now wrapping up How to Get Paid, a book of advice for aspiring entrepreneurs that he hopes to publish next year. LAST YEAR'S RANK No. 20, with $249 million

12 Sean Combs (P. Diddy) CEO/Founder Bad Boy Entertainment WEALTH $293.7 million - AGE 32 He recently bought full control of his record label from Arista, and his Sean John clothing is off the charts. LAST YEAR'S RANK No. 22, with $231 million

13 Joe Liemandt Chairman/CEO/Founder Trilogy WEALTH $250 million - AGE 34 "These are tough times" for his software company, says Liemandt. "Now it's becoming obvious that we made the right choice [not to go public]." LAST YEAR'S RANK No. 14, with $390 million

14 Raul Fernandez Chairman Emeritus Dimension Data North America WEALTH $238 million - AGE 36 Why didn't his wealth fall this year? Says Fernandez, who founded IT company Proxicom in 1991: "I took my money out of the market a few years ago." LAST YEAR'S RANK No. 30, with $188 million

15 Marc Andreessen Chairman/Co-Founder Opsware WEALTH $218 million1 - AGE 31 The Netscape founder says he'll eventually give all his wealth to charity: "If I die with a penny in my bank account, it will have been a miscalculation." LAST YEAR'S RANK No. 38, with $166 million

16 Tiger Woods Golfer WEALTH $212 million - AGE 26 In January, Tiger--still golf's winningest player by far --inked an endorsement contract with Nike for a staggering $100 million over four years. LAST YEAR'S RANK No. 40, with $160 million

17 Jeffrey Citron CEO/Co-Founder Vonage WEALTH $189 million - AGE 32 Now head of a telecom, Citron owes most of his wealth to Datek Online, the Internet stock-trading firm he founded and cashed out of back in 1999. LAST YEAR'S RANK No. 29, with $194 million

18 Nav Sooch Chairman/CEO/Co-Founder Silicon Laboratories WEALTH $186 million - AGE 39 The possibility of being too poor to make next year's list doesn't worry the CEO of this semiconductor maker: "The distressful thing is turning 40." LAST YEAR'S RANK No. 39, with $162 million

19 Pantas Sutardja Director/Co-Founder Marvell Technology Group WEALTH $185 million - AGE 39 Seventy-hour workweeks, says a rep at the Internet data-storage and networking firm, mean Sutardja "has no hobbies and hasn't vacationed since 1995." LAST YEAR'S RANK No. 16, with $363 million

20 Jared Polis Investor and Politician WEALTH $174 million - AGE 27 Polis made a bundle by selling e-greeting-card site Bluemountain.com; now he's launched several ventures and has entered politics (see previous story). NEW THIS YEAR [2]

21 Scott Blum CEO/Founder Buy.com WEALTH $173 million - AGE 38 In 1999 Blum sold his stake in the online retailer he founded; then Buy.com went public, and last fall he reacquired it for a song (see previous story). 1999 rank No. 9, with $1.66 billion

22 Shaquille O'Neal Basketball Player Los Angeles Lakers WEALTH $171 million - AGE 30 Shaq rakes in $21 million for hitting the court this year--more than anyone except Kevin Garnett--and he gets more than $10 million for endorsements. NEW THIS YEAR

23 Elon Musk CEO/Founder Space Exploration Technologies WEALTH $165 million - AGE 31 Musk's wealth zoomed when Paypal, his online-payment service, went public in February (eBay later bought it). Now he wants to make rockets. NEW THIS YEAR

24 David Hitz Executive VP/Co-Founder Network Appliance WEALTH $150 million - AGE 39 Hitz got most of his dough by selling a boatload of Network Appliance stock, which has fallen 96% from its high of $240 in 2000. LAST YEAR'S RANK No. 27, with $202 million

25 Jeffrey Zients Chairman Advisory Board Co. WEALTH $149 million - AGE 35 The successful November IPO of his health-care research and consulting firm puts Zients onto the list for the first time. NEW THIS YEAR

26 Julia Roberts Actress WEALTH $145 million - AGE 34 With 2000's Erin Brockovich, Roberts--the only woman on this year's list--became the first woman to join Hollywood's $20-million-a-picture club. NEW THIS YEAR

27 Halsey Minor Chairman/Founder Grand Central Communications WEALTH $144 million - AGE 37 His venture capital firm 12 Entrepreneuring went under in March; now Minor runs a network-management company. LAST YEAR'S RANK No. 34, with $180.2 million

28 Jeff Mallett Investor WEALTH $142 million - AGE 38 With some of the millions he made selling Yahoo shares, the former COO bought a vineyard, a golf club, and part of the San Francisco Giants. 2000 RANK No. 16, with $805 million

29 Jen-Hsun Huang President/CEO/Co-Founder Nvidia WEALTH $139 million - AGE 39 After an SEC inquiry prompted chipmaker Nvidia to restate profits since 2000, Huang told reporters, "We've learned a lot about accounting." LAST YEAR'S RANK No. 12, with $507 million

30 Jerry Greenberg Co-Chairman/Co-CEO Sapient WEALTH $137 million - AGE 36 This e-consultant's most recent read? Corps Business: 30 Management Principles of the Marines. 2000 RANK No. 11, with $1.47 billion

31 Paul Gauthier Retired WEALTH $132 million - AGE 30 The Inktomi co-founder sold $128 million worth of company stock and disappeared from the corporate world last year. 2000 RANK No. 19, with $693 million

32 Brad Pitt Actor WEALTH $127 million - AGE 38 Adding wife Jennifer Aniston's wealth to Pitt's gives the Hollywood couple a combined net worth of approximately $170 million. NEW THIS YEAR

33 Bobby Kotick Chairman/CEO Activision WEALTH $120.8 million - AGE 39 Lucky Bobby: Stock of Activision, the second-biggest independent videogame publisher in the world, has nearly doubled since last year. NEW THIS YEAR

34 Marc Ewing Publisher Alpinist magazine WEALTH $120.4 million - AGE 33 The Red Hat co-founder traded high tech for low: After a couple of years off, he's launching a magazine about rock climbing (see previous story). 1999 RANK No. 13, with $775 million

35 Andre Agassi Tennis Player WEALTH $120.3 million - AGE 32 The veteran racqueteer is his sport's top endorser, raking in up to $20 million a year from the likes of Nike, Schick, Canon, and Deutsche Bank. NEW THIS YEAR

36 Sudhakar Ravi CTO/Co-Founder SonicWALL WEALTH $119.1 million - AGE 37 He and brother Sreekanth (No. 37) cashed out $87 million each before the stock of their Internet security company fell 77% over the past year. LAST YEAR'S RANK No. 25, with $218.9 million

37 Sreekanth Ravi Chairman/Co-Founder SonicWALL WEALTH $119 million - AGE 36 Sreekanth gave up his CEO role at SonicWALL last October "to enjoy life a little more with his fiancee," says a company spokesperson. LAST YEAR'S RANK No. 26, with $218.7 million

38 Michael Robertson CEO/Founder Lindows WEALTH $117 million - AGE 35 After Vivendi bought his MP3.com last year for $372 million, he started a computer-operating system that vies with Microsoft Windows: "I love competition." 1999 RANK No. 11, with $903 million

39 Will Smith Actor WEALTH $113 million - AGE 33 He's made most of his money from blockbuster movies, but his own production and real estate companies also keep this man in the black. NEW THIS YEAR

40 W. Glen Boyd Retired WEALTH $108 million - AGE 35 Boyd sold Webtrends, an Internet analytics company, in March 2001 and "bought a yacht to circumnavigate the world." NEW THIS YEAR

[1] Our valuation incorporates new information we were able to gather about Andreessen's non-Opsware assets.

[2] We mistakenly omitted Polis from the list last year.