Trains on Metra's Southwest and Heritage Corridor lines were delayed up to one hour on Thursday night detouring around the derailment site.
Eastbound Amtrak trains have also been delayed up to 90 minutes and morning service to St. Louis will be affected.
At 8:53 a.m., four locomotives derailed near 18th and Lumber just south of Union Station. Officials said the trains were en route from a nearby rail yard.
"The switchings are done by a company ... and they were in the process of hooking six engines to two other engines and somehow in the process, the engines started to roll and got away," said Thomas Zapler, Union Pacific Spokesperson.
The wheels of two of the locomotives slipped off the tracks. Two others were leaning. The derailment damaged the tracks and leaked about a gallon of oil into the Chicago River- not the diesel fuel as first thought. No one was hurt.
"The only thing that leaked was a few gallons of oil that's in the engine. No diesel fuel leak, so it really as far as leaking was almost a nonevent," said Thomas Zapler, Union Pacific Spokesperson.
The derailment led to delays for Metra trains that run on the Southwest Line to Orland Park. Officials warned it could take up to 12 hours to fix the tracks and get things back on schedule.
As of 6 p.m. Metra was encouraging commuters to take alternative routes, including the Rock Island line, which will use buses to move passengers to their destinations.
Six evenings trains run along the Southwest Line from Union station between 4:30 and 6:58 p.m. Delays up to an hour are expected.
"Hurry up and rush here at 12:35 to make the train and have to sit for another two hours waiting for the next one," said Cathy Loewe, commuter.
"I'm trying to make the best. I've got a place to sit," said George Biondic, commuter.
"I had taken off half a day to go for eye doctor appointment, and now I am delayed quite a bit. So it kind of ruins my day a little bit," said Sara O'Malley, commuter.
Outbound trains from Union Station:
The following inbound trains will be departing all outlying stations on time but will arrive at Chicago Union Station 45 to 60 minutes late:
Check with the Metra website, metrarail.com for specific train updates.