What happened

A bending-stress fatigue crack at a bad weld ruptured the 36-inch Keystone Cushing Extension pipeline, releasing nearly 13,000 barrels (about 543,000 gallons) of heavy crude over land and into Mill Creek — the largest release in Keystone system history and the largest US inland spill since 2013. Oil coated the creek bank-to-bank for 3.5 miles and killed or affected more than 2,700 animals. The operator agreed to pay a $26.9 million civil penalty plus roughly $40 million in prevention measures in a 2026 settlement. This was an accidental pipeline failure, not an attack.

When cited sources give different casualty, damage or spill figures for this event, they’re reported side by side above rather than merged into one number. See how confidence levels work.