International Olympic Committee (IOC) chiefs begin a round of visits next week to the bidding cities - Beijing, Osaka in Japan, Toronto, Istanbul and Paris - before writing a key evaluation report on their bids.
But few experts are prepared to predict the outcome of July's vote in Moscow.
Certainly, Beijing, who want to take the Olympics to China for the first time, are regarded by many as the front-runners. But some IOC followers believe Toronto and Paris are catching up the Chinese fast.
Olympic campaigns are rarely easy to call.
The last time the IOC decided on the venue of a Summer Games, in 1997, many experts thought Rome was the clear favourite to beat Athens in the 2004 bidding. But the Greeks gained a lot of ground in the last few months of the campaign and won.
Predicting the voting patterns of an organisation such as the IOC, where internal politics play an important role, is a complicated issue.
This year's 2008 vote is also being overshadowed by the campaign to succeed Juan Antonio Samaranch as president which will be decided in a vote of all IOC members in Moscow.
The IOC's evaluation commission, which studies the technical strengths of each bid, will start its series of visits with a four-day trip to China on February 21. The team will go on to Osaka from February 26-28, then to Toronto (March 8-11), Istanbul (21-24) and Paris (March 26-29).
The commission, chaired by leading cycling official Hein Verbruggen, is made up of representatives of the IOC, National Olympic Committees, athletes and experts from outside sport.
In mid-May it will publish a detailed report on its findings which will be given to IOC members before they vote on July 13.
The report has taken on more importance since the 2004 decision.
IOC members themselves used to visit the bidding cities. But they have been banned from doing so since the 1998 Salt Lake City bribery scandal which led to 10 members leaving the organisation after breaking rules on accepting gifts from the U.S. city when it was successfully bidding to stage the 2002 Winter Games.
At the end of last year Samaranch warned the five 2008 candidates about the new anti-corruption rules banning visits and gifts when they made brief presentations to the IOC's ruling executive board.
So IOC members will have to rely on the commission's report for their main insight into the bids.
But the city with the best report is still not guaranteed the Games because complex sports politics will also play a crucial role.
Beijing has a strong case. Boasting fluent English speakers on their bid team, the Chinese appeared professional and slick in their brief presentation to IOC leaders and the media in December.
The opportunity to expand business in the Chinese market could prove attractive to the blue-chip sponsors who back the Games.
But China's human rights record could enter the equation, with memories of the 1989 massacre of student protesters in Tiananmen Square and more recent crackdowns on the Falun Gong spiritual movement.
Any flare-up of controversy in the next few months could mean Beijing losing ground and Toronto and Paris have been working hard to pounce.
The IOC needs to make a safe decision this time.
Although last year's Sydney Olympics were a resounding success, the build-up to the 2004 Games has been surrounded by controversy with concerns about security, transport and construction of some of the facilities.
Samaranch gave the Greek organisers a severe warning last year because he felt they were dragging their feet on organisational issues.
Paris has the disadvantage of being on the same continent as Athens. Members may be reluctant to hold the Games in Europe again immediately after 2004 and the French could have a much stronger case for the 2012 Games.
This time could therefore be a dry run for Paris but the French capital is bidding hard and could still pull off a surprise.
Toronto also appears to have a good chance and many believe it will receive a solid evaluation report.
The Canadians have the advantage of time - North American time, that is.
Sydney produced disappointing ratings for NBC, the television network which pays out millions of dollars for the U.S. television rights for the Games. The huge time difference meant NBC concentrated on highlights packages instead of live action.
The present rights contract with NBC runs until 2008. The prospect of being able to hand the U.S. network live coverage in the last Games of the contract could be very appetising to the IOC at a time when they will be looking to seal a new deal beyond 2008.
Istanbul and Osaka are regarded as outsiders to win. It would be a huge surprise if either city made it to the last round of voting.
Reuters
Even the most experienced Olympic observers cannot agree on which city will win the battle to stage the 2008 Summer Games as the deciding vote draws near.
