Chopper7HD was live over the scene Wednesday night, where fire crews were seen pouring water on what appears to be one of the tankers at the plant.
The refinery is near 135th and New Avenue. Authorities say the fire began around 7:45 p.m. A resident who lives nearby said thick black smoke was billowing over his home around 8:30 p.m.
"My main concern right now is the quality of the area coming over this area right now," said Joe Ebert, nearby resident.
There are no reports of injuries so far, but ambulances are being sent to the plant in Lemont. No evacuations have been required, according to Citgo officials.
There is no official word yet on the cause of the fire, but an employee who said he was working inside the refinery said crews were working on a valve when there was a leak of crude oil that ended up catching on fire.
Citgo says it is conducting air quality monitoring in the area and is working with Will County authorities.