The report may offer some clues about the decision.
For nearly a week in early April, Chicago's bid team sat face-to-face answering hundreds of questions from the International Olympic Committee evaluators before taking them on an 11 hour tour of the city's proposed venues.
The report is the result of that visit, and others just like it to Rio, Madrid and Tokyo.
"The bid is a strong one but at the end there is only one winner," said Nawal El Moutawakel, IOC Evaluation Commission Chair.
An IOC source tells ABC 7 the report is fairly flattering to all of the candidate cities. It concludes all four are capable of hosting the Games. It prods each of the cities to ensure "good, effective leaders" are selected to run the Olympic Organizing Committee.
The report, we're told, will praise Chicago's compact, downtown venue plan. But it takes issue with Chicago's mass transit system, specifically aging rail lines that don't carry anywhere near the capacity required to carry the estimated four million people who would attend an Olympic Games in Chicago along with regular commuters.
By comparison, the report praises Tokyo and its modern rail system which carries 20 million people a day.
Our source says the report also points out Mayor Daley's initial hesitation to signing the host city agreement which could put Chicago taxpayers on the hook if the Olympic budget is blown. But a poll commissioned by International Olympic Committee in February revealed what our source calls "strong support" among Chicagoans for bringing the Games to town.
"I can't forecast what's in there but I do know we've addressed about everything. I'll be shocked if there's anything really major," said Patrick Ryan, Chicago 2016 Chairman. "If you have more work to do you're probably in trouble."
The IOC report does not rank Chicago, Rio, Madrid and Tokyo or even mandate changes be made to their Olympic plans. Instead, it's meant to be an objective, dispassionate look at how each city would host the games. The reality is most IOC members will read it and then vote based on emotions, allegiances or politics.