NEW YORK (CNN/Money) - Dozens of U.S. athletes won gold medals at the Olympics that wrapped up Sunday in Athens. But only a fraction of those winners are likely to strike advertising gold after the games.

U.S. swimmer Michael Phelps, shown here in a Visa ad, is one of the Olympians who arrived in Athens already having won advertising gold.

Part of the problem for the winners is that most Olympic athletes are virtually unknown. Even those who spent two weeks in the media spotlight will have little in the way of exposure for the next four years.

For all his magazine covers before the start of the games, U.S. swimmer Michael Phelps was probably less well-known when he arrived in Athens than the average star athlete from a major team sport. And few Americans will see him compete again before he dives into a pool in Beijing in 2008.

But Phelps -- who won six gold and two bronze medals -- was able to score advertising gold before he put a toe in the water in Athens. He signed seven deals, some with top-line national advertisers such as Visa, Omega watches and AT&T Wireless.

"They (sponsors) want to buy while the property is cheap," said Jeff Chown, managing director of The Marketing Arm, which arranges endorsement deals between advertisers and athletes. "Both sides have a risk. He's got a risk taking deals not lucrative enough if he does exceptionally well. If he doesn't do well, the brands have probably overpaid."

Even though Phelps fell just short of the 32-year-old, seven gold medal mark of Mark Spitz, his sponsors got their money's worth. One executive with Visa, which has the 19-year old Phelps under contract through 2008, expressed regret to reporters that the credit card issuer hadn't signed him through 2012.

Phelps is not alone among favorites who marched in the opening ceremonies knowing they're already winners in the endorsement race.

Even before the opening ceremonies begin, many Olympic athletes have already turned potential gold into green by signing sponsorship deals. Great for the athletes, but sometimes a risky bet for the companies. CNNfn's J.J. Ramberg reports. Play video (Real or Windows Media)

"Those that are expected to win individual gold medals in compelling sports should have a couple of deals going into games," said Peter Carlisle, agent for Phelps and head of the Olympic and action unit of sports marketing firm Octagon. "If they do well, there will be a deal or two after the games."

Beach volleyball gold medal winners Kerri Walsh and Misty May got a lot of attention in their match Aug. 24, but fewer Americans saw it than saw the pair playing in the snow in a Visa commercial that aired on this year's Super Bowl.

What's important for an athlete's marketability is being able to break through a zillion hours of coverage on NBC and its cable affiliates with a compelling story in a popular sport, such as swimming, gymnastics or track and field.

"If you're a gold medal archer, unless you have an unbelievable story, you probably won't have deals," said Carlisle.

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Few deals are hammered out in Athens, according to Carlisle, even for those who win early the two-week competition. But deals will start to be announced soon after the athletes return home. The top deals for the most marketable athletes are likely to be in the millions of dollars.

For athletes who come to Athens without deals in their pockets, far more modest deals likely await, even if they ended up with gold medals.

"A lot of these athletes, their objective is to sustain their quest for the next Olympics, not having to work at a job that distracts them," said Carlisle. Modest, five- or six-figure deals are enough for them.

Another Carlisle client with deals on the books when she arrived in Athens was Jennie Finch, a pitcher for the gold medal winning U.S. softball team, who has unusual appeal for a team sport athlete. Her deals include Sprint and Bank of America.

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The fact that she was picked by People Magazine as one of the "50 Most Beautiful People" and selected "World's Sexiest Athlete" in an ESPN poll certainly helped her, her agent conceded. She won't be the only athlete whose appearance will affect the dollars coming her way.

Sex appeal was one factor that helped softball pitcher Jennie Finch break out of the pack with advertisers.

Eight female athletes who have competed in Olympics or trials, including two members of this year's U.S. team -- high jumper Amy Acuff and swimmer Haley Cope -- posed nude in the September issue of Playboy.

Both Acuff, who finished fourth in the high jump Saturday, and Cope, who won a silver after swimming in a preliminary heat of the women's medley relay, also appear on the cover of the men's magazine FHM (with a number of other Olympic athletes). They also show up in slightly less revealing poses inside that magazine.

Finch told the show, "Access Hollywood," that she turned down lucrative offers to pose nude. But playing up sex appeal is one of the keys for athletes who want to catch the attention of advertisers.

"The last layer in determining marketability is whether the athlete is good looking," said Kenneth Shropshire, a professor at the University of Pennsylvania's Wharton School. "The great advantage that many swimmers have is they are very fit individuals who are almost fully exposed."

Two members of the U.S. Olympic team posed nude in the September issue of Playboy.

Carlisle thinks the athletes who posed nude are not likely to get deals from mainstream advertisers. But the women who posed were probably not going to get that kind of Coca-Cola/McDonald's/Visa type of ad anyway.

"There will be some resistance from traditional Olympic marketers," he said. "It might help them get a deal with an advertiser who wants something a bit edgier."

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Of course the Olympians with some of the greatest advertiser appeal are the professional athletes who made the trip, due to the greater exposure they'll get over the next four years. Experts say the marketability of the National Basketball Association players who played for the much maligned U.S. team were not hurt by their team going home with three losses and only a bronze medal.

"People maybe scratching their head, but (Philadelphia 76ers star Allen) Iverson doesn't lose his Reebok deal as a result," said Shropshire.