An oil pipeline in North Dakota spilled nearly 200,000 gallons of petroleum into a nearby creek last week without its early warning sensors ringing the alarm, the company that owns the pipeline said Monday.

The Belle Fourche Pipeline was reported leaking oil nearly one week ago after a landowner discovered the oil in a creek. The Casper, Wyo., company True Cos., which operates the pipeline, said that electronic sensors connected to the pipeline did not detect the leak.