TC Energy’s TRP-T Keystone oil pipeline is offline due to operational issues, cutting off a major conduit of Canadian oil to the United States, three industry sources said on Thursday.

The 622,000 barrel-per-day pipeline has been dogged by problems, including a 2022 spill in rural Kansas.

Calgary, Alberta-based TC did not immediately respond to a request for comment.

TC shares were slightly higher in Toronto.

Keystone, stretching 4,850 km (3,000 miles), transports oil from Alberta to Nebraska, where it splits, with one arm running east to the Midwest and the other running south to the U.S. crude storage hub in Cushing, Oklahoma and to the Gulf, where it is processed by refiners or exported.

Last year, TC said it planned to spin off its liquids business, including Keystone, to focus on transporting natural gas. The company has been selling assets to reduce debt.