Five cars of a train carrying crude oil derailed Friday morning at King of Prussia rail yard but no oil spilled, the railroad said.

The cars went off the tracks at Norfolk Southern's Abrams Yard on Henderson Road about 4:30 a.m., said Dave Pidgeon, a spokesman for the rail company.

The cars were carrying a heavy form of crude oil and crews are working to rerail them, he said.

As of early Friday afternoon, two cars were upright, two were leaning and one was on its side.

Pidgeon said nothing spilled or leaked in the incident.

The cause of the derailment remains under investigation. The incident happened inside the rail yard, so other rail traffic wasn't affected.