Mounties say the oil truck was leaking for about an 11-kilometre stretch on the Yellowhead Highway near Kitscoty.
They say it appears the driver had failed to properly close a valve on the tanker.
There were no collisions or injuries reported, although police say the amount of oil leaked in some areas was significant.
Charges have been laid against the driver under the Dangerous Goods and Transportation Act.
Police say Environment Canada has been notified and environmental charges against the company are pending.
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