TransCanada Corp. says the Keystone pipeline will likely remain shut down for the rest of the week while officials investigate an apparent oil spill in southeastern South Dakota.

Oil was discovered on a 27.9-square-metre area in a ditch near a Freeman, S.D.-area pump station. About 100 workers are at the site removing soil and determining the location of the leak. A company spokesman says crews have found no pipeline damage. TransCanada hasn't released the amount of oil or speculated on cleanup costs.

TransCanada says it has found no significant harm to the environment. State environmental officials are monitoring the cleanup.

The Keystone pipeline runs from Alberta to refineries in Illinois and Oklahoma, passing through the eastern Dakotas, Nebraska, Kansas and Missouri.

Freeman is about 64 kilometres southwest of Sioux Falls.