BISMARCK — The operator of a portion of the Keystone pipeline that runs through North Dakota estimates about 3,500 barrels, or 147,000 gallons, of crude oil spilled into a field near Fort Ransom Tuesday, April 8, after a pipeline malfunction.

Trucks and workers started a cleanup effort at the site of a spill of the Keystone oil pipeline in rural North Dakota

An estimated 3,500 barrels of oil spilled in a field near Fort Ransom, N.D., and the release was contained, the pipeline’s operator said.