Undetected errors during construction and manufacturing led to the two largest spills in the history of TC Energy Corp.’s Keystone crude oil pipeline system in 2017 and 2019, according to a report by the Government Accountability Office (GAO).

keystone route

The 2,687-mile system has transported more than 3 billion bbl of oilsands crude from Canada to Gulf Coast refineries since it began operating in 2010.

Democratic Reps. Rep. Peter DeFazio (OR) and Frank Pallone Jr. (NJ) requested the GAO report in November 2019 in response to the two large spills, and amid heated debate over the Keystone XL pipeline, which has since been scrapped.

Keystone XL would have added up to 830,000 b/d of transport capacity to the Keystone system, which allows Canadian oilsands crude to reach refiners on the...