Track star Usain Bolt is set to race ahead of many of his fellow Olympians with new endorsement deals, after cementing his position as the world's fastest man with back-to-back gold medals in the premier track and field event. Only American sprinter Carl Lewis had previously achieved such a feat.

"That 10 seconds is worth $2 million a second, for the next 12 months easy," said Australian celebrity agent Max Markson, who believes the Jamaican will double his sponsorship earnings after the winning sprint in London.

The 25-year-old is already the highest-paid Olympian - outside of basketball and tennis - at this year Games with estimated earnings of $US20.3 million ($19.2 million) over the past year, according to US business magazine Forbes in a report last month.

Bolt's biggest sponsor, Puma, forks out $US9 million annually for the track star. But it was his 2008 triumph in Beijing that saw many other sponsors outside the field of athletics, such as watchmaker Hublot, communications company Virgin Media, car manufacturer Nissan, credit card giant Visa and Soul Electronic jump on the Bolt bandwagon, Forbes reported.

"Generally speaking the larger the audience and bigger appeal an athlete commands, the higher their commercial value and size of the endorsement deals they should expect to net," Chris Styring, the general manager of research company Sweeney Sports and Entertainment, told Fairfax.

"Athletes such as Roger Federer and Usain Bolt who compete at the highest levels in sports that are easily accessible, globally broadcast on free-to-air channels and appeal to both genders will generate big off-track deals."

Jessica Ennis, hailed as the face of Team Great Britain, lived up to the hype when she took home gold in the women's heptathlon on Saturday.

The 26-year-old British track athlete is set to improve on her £1 million ($1.48 million) sponsorship deals with British Airways, Jaguar and Olay, but experts say there is less money in women's sport - and in track-and-field in general.

"Her advisers and management need to work very, very carefully now as commercially, she is very, very valuable," Professor Simon Chadwick of Coventry University's Business School told the London Evening Standard.

"I think for Ennis to earn the same amount as say, Andy Murray, she's going to have to get a much more global profile and typically female athletes just don't have that kind of international profile.

"In relation to male athletes she's not about to go stratospheric but in relation to domestic female athletes she is. She'll be rich, there's no doubt about it, but if she was a man she'd be richer."

n the pool, history's most decorated Olympian - US swimmer Michael Phelps, 27 - did not even make Forbes' Top 20 highest-paid Olympic athletes with his estimated $US7 million of endorsement deals from 11 sponsors such as Omega, Visa and Speedo.

His US compatriot and rival, 28-year-old Ryan Lochte, is estimated by Forbes to have pulled in about $US2 million in the past year from sponsors such as AT&T, Gillette and Nissan.

In the meantime, their 17-year-old teammate Missy Franklin, already dubbed the "female Michael Phelps" for her golden turns in the aquatic centre, has turned down the chance of securing what experts said could be millions of dollars in sponsorships to remain an amateur swimmer, US network ABC reported last week.

Her decision was praised by US sports marketing expert Ronald Oswalt, who told ABC: "Winning a gold medal can be priceless, but cashing in on the glory could or couldn't turn into happiness.

"So many parents push their kids. They think the Olympics are going to be their payday, but her dreams have already come true."

Yet many other Olympic athletes struggle financially. Without a gold medal to their name, securing an endorsement deal can be difficult, San Diego State University's Professor of Marketing George Belch told The Arizona Republic newspaper.

"I'm pressed to think about people who've been runners-up and have gotten much attention. Gusty performances and overcoming injuries can make for great stories, but even then it's very difficult [to get an endorsement deal] without the gold," he said.

"It's really a huge sacrifice these athletes are going through just to even make the team, let alone medal. They forgo numerous career opportunities while cramming into apartments for eight to 10 years doing odd jobs and living hand to mouth."

Ultimately, the Olympics, despite its global appeal, does not necessarily give its athletes the same worldwide recognition as professional sports such as basketball, tennis and golf, Mr Markson said.

Michael Phelps ... images of some of the medals the US swimmer has won at various Olympic Games.

While Bolt's repeated success on the track and field stage will "propel him to another level", Markson said he did not think "globally amongst the general public he has the presence of say a Michael Jordan, a Mike Tyson or a Tiger Woods".

"Track and field is not as big a sport as basketball in America, boxing worldwide and golf worldwide. He's not on the same scale as a Tiger Woods or Jordan, who literally earned hundreds of million of dollars."