The 622,000 barrel-per-day pipeline is a critical artery shipping heavy Canadian crude from Alberta to refiners in the U.S. Midwest and the Gulf Coast. It is unclear how long the closure will last.

There have been several spills on the line since it began operating in 2010. The following is a timeline of some of Keystone's biggest oil spills, based on data from the U.S. Pipeline and Hazardous Materials Safety Administration.

2011

May: TC shut the pipeline for six days after a spill of about 500
barrels of oil due to a failed fitting at a North Dakota pumping station. https://reut.rs/3iKr5JC

2016

April: TC shut down the pipeline
after about 400 barrels of oil leaked in Hutchinson County, South Dakota. https://reut.rs/3W2FjUx

2017

November: TC shut part of the Keystone pipeline system after a leak in South Dakota, caused by mechanical damage from original construction. Originally pegged at 5,000
barrels, a TC spokesperson later put the estimate at about 9,700 barrels. https://reut.rs/3P9J6Nu

2019

February: Portions of the Keystone pipeline were shut down afte
r 42 barrels of oil leaked on land in rural St. Charles County, Missouri. https://reut.rs/3HkTBLZ

October: An estimated 9,120 barrels of oil spilled in North Dakota. The spill was one of the biggest onshore crude sp
ills in the last decade and the largest for Keystone, according to PHMSA. https://reut.rs/3Hq4zjH

(Reporting by Ruhi Soni, Arshreet Singh and Sourasis Bose in Bengaluru; Editing by Shounak Dasgupta)