The second leak in two years along the Keystone pipeline was discovered in North Dakota Tuesday night.
Business Insider reports the leak spilled half an Olympic-sized swimming pool's worth of crude oil onto a wetlands area.
Crews shut down the pipeline, which extends through 7 US states and into Canada.
TC Energy owns the pipeline, estimates about 383,000 gallons, or more than 9,000 barrels of oil, were spilled.
The company has yet to determine publicly what caused the leak to occur.