CHICAGO -- The City Council unanimously agreed Wednesday to take full financial responsibility if Chicago is awarded the 2016 Summer Olympics, a guarantee the local bid leader said leveled the field because the other three candidates already have government backing.

The council voted 49-0 to authorize Mayor Richard Daley to sign the International Olympic Committee's host city contract that puts taxpayers on the hook for the Olympics and a proposed $4.8 billion operating budget.

"We are joining the ranks of the other three so that no longer will we be at a competitive disadvantage by virtue of this so-called guarantee," Chicago bid leader Patrick Ryan said after the council vote.

Financial guarantees have been a recurring issue for Chicago as it bids against Tokyo, Madrid and Rio de Janeiro. The IOC will pick the host city at its Oct. 2 meeting in Copenhagen.

Daley needed the council's approval after promising to sign the IOC contract in June to allay any concerns about the city's commitment. An IOC evaluation report had rapped the city bid for not providing a full financial guarantee.

Several aldermen said they could approve the contract while minimizing the risk to taxpayers because local bid officials have lined up more than $1.4 billion in insurance to protect the operating budget.

"[It] really gives those of us in government confidence that there's a real layer of protection between us and the necessity for putting in any either city or state resources," Aldermen Toni Preckwinkle said.

The Olympics have a history of costing more than what was planned. London's budget for the 2012 Games has grown to more than $16.5 billion, double what was originally forecast. And Montreal ran up massive debts when it hosted the 1976 Games that took decades to pay off. The IOC has offered to help the 2010 Vancouver Games cover any deficit because of the global economic downturn.

Some aldermen who had been skeptical of the Olympics wound up supporting the host contract decision because they see the Games as an economic engine to help Chicago pull itself out of tough economic times.

A group that opposes Chicago's bid said aldermen abdicated their responsibility to taxpayers.

"The City Council endorsed the mayor's blank check to the 2016 Olympic bid," said Tom Tresser, a spokesman for No Games Chicago.

Alderman Joe Moore also acknowledged some cynicism remains because of the city's reputation for shady backroom deals.

"While our city can boast a vibrant economy and a beautiful scenic lakefront and a wonderful diverse culture, it also unfortunately bears the ugly stain of political corruption and favoritism and a history of projects with cost overruns," Moore said.

The ordinance approved Wednesday also includes oversight of the Olympics should the city get the Games, including financial reporting and insurance updates. Moore said he would have liked to have seen more independent oversight.