TransCanada Corp said on Thursday it has shut down its major pipeline for moving Canadian crude oil from Alberta to the U.S. Midwest and Midcontinent after detecting a “small anomaly” on the pipe, pushing up benchmark oil prices.

TransCanada said the 590,000 barrel a day Keystone pipeline is expected to be shut for three days as crews investigate the pipe. It said the potential defect was discovered on Wednesday by an in-line inspection tool and no leaks were found.

The pipeline has the capacity to transport a quarter of Canada’s crude oil exports to the United States.

(Inside Climate News)