George Clooney suffered a spinal injury during a stunt. Due to the weight he gained for his role, the injury left him bedridden for a month and caused severe migraines, which prevented him from doing publicity for Ocean's Twelve (2004). The injury was eventually corrected with surgery. Clooney has since called his weight gain "pretty stupid".
In the days leading up to the Oscar nominations, the Academy announced that the film's screenplay was considered original, not adapted. Since it had been strongly advertised as adapted, many believed the film would not be nominated. It was nominated for Best Original Screenplay, but lost to Crash (2004).
Michelle Monaghan originally had a substantial role in the film, playing Miss USA who becomes involved with a rich Arab oilman. But her entire sub-plot was cut when the film seemed too long and complicated for review audiences.
"Bob Barnes" - the character portrayed by George Clooney in the film "Syriana", is based on the real life exploits of career CIA operative Bob Baer. Baer spent 21 years as a CIA man hunter. Mr. Baer is the lead investigator on the History Channnel's popular TV series "Hunting Hitler". Season 3 is due to air in late 2017. Source: These details are stated by Baer in the opening team overview/background of both Season 1 and Season 2 of the program.
Roger Ebert's theory about the film's Byzantine oil-related plotlines was that the U.S. and China had a secret deal to buy up and ship oil from Kazakhstan without actually drilling for any of it, and that the film's merger was a paper deal to provide legal cover for these actions.
In two clever examples of parallelism in the script and dialogue, CIA staffer Fred Franks uses the phrase "Help me out here" in the film after it's been directed at him by his CIA supervisor, Terry. And the name "Jimmy" is one that Bob Barnes insists on using when he talks to Mussawi -who's offended by it - but it's a name that Killen CEO Jimmy Pope invites Bennett Holiday to use in addressing him.