With 13 IOC delegates due to tour Chicago this week, the US city is working to build on advantages that include the backing of President Barack Obama and past successful US games, analysts who follow the Olympics said.
After Chicago, IOC delegates will visit the other bidders: Madrid, Rio and Tokyo. The jockeying will continue until the final vote in Copenhagen on October 2.
"There is no bid that has a greater chance than Chicago, but there are many ways that Chicago may not be selected," said Marc Ganis, president of Chicago sports consulting firm Sportscorp Ltd.
Analysts said London won the bidding for the 2012 games over favoured Paris, while underdog Sochi, Russia, was awarded the 2014 Winter Olympics. Both cities' bids were helped when their respective leaders, Tony Blair and Vladimir Putin, showed up at the final vote to lobby the delegates.
Similarly, Obama could be "the X factor" if he goes to Denmark in the fall, analysts said.
"If Barack Obama shows up, it could turn the tide," said Kelly Crabb, an attorney whose firm was international counsel for the Beijing Olympic Organising Committee.
Other factors favouring Chicago: the last US games were in 1996 in Atlanta and the United States is the world's biggest media market.
"As important as it is to rotate the Olympics around the world, it's also vitally important for the continuation of the Olympic movement to have the Summer Olympics in the US at least every 20 years or so," Ganis said.
Working against the US city is its lower level of financial guarantees compared with the other three bids, all of which include assurances that any cost overruns will be covered. The city of Chicago and the state of Illinois combined have pledged $750 million against any operating deficits.
IOC chief Jacques Rogge seemed to dismiss that worry last week when he said he was sure Chicago would be able to deliver with a strong guarantee.
Another factor is an IOC desire for the US Olympic Committee to share more of its share of the revenue generated by the Olympics, analysts said. While a framework of a deal was reached last week, that issue could still wrankle some IOC delegates.
The IOC recognises the potential value of a Chicago Olympics, however, as it has delayed asking for bids for the 2016 broadcast rights until after the city selection, analysts said. A Chicago victory would likely result in more bidders and a more lucrative deal.
Several analysts see Tokyo as the main threat because the Beijing Olympics last summer proved TV ratings for events in Asia could be huge despite the time difference, while Rio officials stress that the Olympics have never been held in South America.
In the end, a final decision by the 100 or so IOC delegates likely to vote in the initial rounds will also be made partly based on emotion as all four cities offer strong bids.