Salvatore Di Nolfi / AP

IOC President Jacques Rogge, left, says the voting for the 2016 Games will be extremely close.

Chicago overcame one of its biggest hurdles when the city council approved all financial guarantees for the games, clearing the way for Mayor Richard M. Daley to sign the host city contract if Chicago wins. That was a major step for a U.S. bid city, which — unlike rival candidates — can’t rely on federal government financial backing.

Yet the Chicago bid could still be affected by lingering anti-U.S. sentiment in the European-dominated IOC and resentment over contentious issues with the U.S. Olympic Committee, including the American body’s share of Olympic revenues and plans — now on hold — for its own Olympic television network.

British bookmakers list Chicago as an odds-on favorite, followed by Rio, Tokyo and Madrid.

But Rio seemed to pick up the unofficial front-runner’s tag in June when the bid cities made presentations to IOC members in a specially arranged meeting in Lausanne, Switzerland. Rio officials made a splash by unveiling a big world map with dots showing where all the Olympics have been held — and an empty space for South America.

Brazil also claims it is a growing financial power that has been less affected by the global downturn than the other bid countries. It also cites the experience of hosting the 2007 Pan American Games and Brazil’s selection as host of the 2014 World Cup, an event which could help prepare infrastructure for the Olympics two years later.

Geography often plays a big role, though the IOC has no official policy of geographical rotation of the games.

Tokyo, which hosted the 1964 Olympics, offers a first-class technical bid and claims it is the safest bet at a time of financial uncertainty and already has $4 billion in the bank for the games. Yet, there is a sense among some IOC members that it would be soon to go back to Asia after last year’s stunning Beijing Olympics.

Madrid, which is bidding for a second straight time after a failed attempt for the 2012 Games, also has a strong candidacy with 77 percent of venues already in place. However, it must contend with a reluctance to return to Europe after London in 2012 and Sochi in 2014.

“Although there is no geographical rotation, I think there is a feeling that the games might go west,” British IOC member Craig Reedie said. “In which case, you have a choice of two Western Hemisphere cities (Chicago and Rio). The emotional argument is with Rio with regards to the games having never been in South America before.”

The result could also hinge on the vagaries of the IOC voting system. Ninety-nine of the IOC’s 106 members are eligible to vote in the first round (members from countries with bid cities can’t vote while their candidate is still in contention).

The city receiving the fewest votes is eliminated after each round until one candidate secures a majority. The vote is expected to go the maximum three rounds.

Some members tend to vote out of sympathy in the first round, which can produce some surprises. The key to victory is picking up votes from the cities which go out.

If Tokyo were to go out in the first round, it is believed many of its votes would go to Chicago. If Madrid goes out, the consensus is they would go to Rio.

“The real issue for all four cities is to make sure that as far as they can their committed friends vote for them right from round one,” Reedie said. “There is danger to all four cities in the first round. After that I’m afraid I have no idea where people might go.”

The final 45-minute presentations — featuring speeches and videos — also have a role. The consensus is a city doesn’t win because of a good presentation, but could lose because of a bad one.

For the first time, there are no IOC executive board meetings in the days leading up to the vote. That means there will be much less opportunity for lobbying and schmoozing. Most IOC members won’t be arriving until the day before the vote.

Each city will be bringing celebrity supporters to Copenhagen, including Pele for Brazil and talk show queen Oprah Winfrey for Chicago.

In the end, Rogge said, it will all come down to which bid organizers the members trust most.

“Everything being equal between the four candidates,” he said, “I think it’s the human factor that will be most important.”