Most Olympic athletes don't earn anything for competing in the Olympic Games, but there are notable exceptions. While many can only hope to have their travel expenses paid for - often by corporate sponsors or private donors - some athletes will be raking it in at the London Olympics, which kick off on Friday night.
Governments don't tend to contribute much financially, so athletes rely mostly on the generosity of wealthy individuals and corporate sponsors. However some governments like the US and Russia pay "medal bonuses" for each medal won.
The United States Olympic Committee has rewarded its medal winners with prize money since 1984, and now pays $25,000 for a Gold, $15,000 to those who take home a Silver and $10,000 for a Bronze. On top of that, there could be additional prize money paid by some of the richer US sport federations - and obviously, corporate endorsements and sponsor bonuses for wins and records follow. Canadians were paid for winning medals - up to $20,000 per medal - for the first time at the 2008 Summer Games in Beijing.
By contrast, there are no cash incentives for Team GB to win medals at the London games.
According to this table, which was published in the Daily Telegraph earlier this year, the Italian Olympic Committee is the most generous - promising its gold medallists £116,000 per medal.
National Olympic association bonuses for gold medals (excludes private sponsorship deals)
South Korea* £22,000
Great Britain £0
*Figure relates to bonus paid after the Beijing 2008 Olympic Games
While Usain Bolt is expected to be the biggest star of the London Olympics, it looks like Roger Federer will be the best paid. The Swiss tennis star and world number one, who is worth an estimated $300 million, is the fifth-richest sportsman on the planet, and the second-richest in Europe, behind Formula One driver Michael Schumacher. He will be chasing the one title in tennis that still eludes him: an Olympic Gold medal in the men's singles.
The second-best paid Olympian, according to Top Money, is Team USA's NBA legend Kobe Bryant, who has amassed a fortune of $300 million. He appears to have saved his 11-year marriage, after his wife Vanessa filed for divorce in December but then had second thoughts. The five-times NBA champion, 33, is in London for a final shot at Olympic gold with the USA men's basketball squad.
Meanwhile, Michael Phelps is swimming in a fortune of over $100 million. The American swimmer - who was diagnosed with attention deficit hyperactivity disorder at the age of 9 - has turned his surplus energy to good use and won a record 14 Olympic gold medals, including eight at the 2008 Beijing Games (for which he took home a $200,000 cheque from the United States Olympic Committee).
If Phelps wins three more medals, he becomes the most decorated Olympian of all time - in any sport. He is expected to swim seven events in London in an attempt to outdo Soviet gymnast Larisa Latynina who won a record 18 medals between the 1956 and 1964 Olympics.
The 25-year-old Russian tennis star Maria Sharapova, with a $90 million fortune, will also be one of the highest-paid Olympians. She is the 10th woman to win four Grand Slams in her career, but was knocked out of Wimbledon in the fourth round this year, which cost her the world's women's number one title. But she remains the world's richest sportswoman, thanks to earnings on and off the court from fashion and other endorsements.
And the world's fastest man, Bolt, can look forward to 2012 earnings of $20 million. The Jamaican sprinter has won three Olympic Gold medals as well as three Golds and two Silvers at the World Championships. He has broken his own record in the 100m sprint twice. He gets little from prize money, but makes millions from endorsements and sponsor bonuses for record race times. His biggest sponsorship deal is with Puma, which pays him about $9 million a year.
Had David Beckham been selected for the Team GB squad to play in his home city this summer, he would have jointed the ranks of the best paid Olympians. With a $259 million fortune the former England captain, who now plays for LA Galaxy, topped Britain's Sunday Times Sport Rich List this year.