Crews have shut down the Keystone pipeline after an estimated 5,000 barrels of oil leaked in South Dakota.
TransCanada said in its statement that it expected the pipeline to remain shut down as the company responds to the leak.
According to a press release from TransCanada, which operates the controversial pipeline, the section of pipeline was "completely isolated within 15 minutes and emergency response procedures were activated".
Crews shut down the pipeline Thursday morning and officials are investigating the cause of the leak.
About 5,000 barrels of oil spilled Thursday. It already had been approved by most of the states along the route.
The pipeline transports crude from Alberta, Canada, to refineries in IL and Oklahoma, passing through the eastern Dakotas, Nebraska, Kansas and Missouri.
The company said the spill occurred on private land near Amherst and Britton, S.D., which about 35 miles northeast of Aberdeen and only about 20 miles south of the North Dakota border.
The same pipeline leaked about 17,000 gallons previous year near Freeman, South Dakota. The substance flowing through the Keystone pipeline is known as diluted bitumen, or "dilbit", because the bitumen (the crude oil itself) is so thick and sticky it must be diluted in order to effectively flow through the system.
The company says that it is providing state and federal regulators "with accurate and confirmed information on an ongoing basis".
The Keystone XL pipeline got federal US approval in March when President Donald Trump overturned former President Barack Obama's rejection of the project in 2015. The project has received needed approvals in states between Alberta, Canada, and Nebraska. The PSC will announce its long-awaited decision on the application Monday.