More than 6,000 barrels of oil has seeped from four sites at the Cold Lake Air Weapons Range in Alberta province since May.
An Alberta regulator ordered the company to stop injecting high-pressure steam into a well in an effort to control the leaks, though the incident is ongoing. The company used steam to heat heavy Canadian oil, dubbed tar sands, to make it easier for it to flow out of underground wells.
The company said Wednesday it was working with Alberta regulators to ensure cleanup and land reclamation is done right. It said the seepage was confined to the immediate site and the release from all four areas is less than 20 barrels per day.
"Canadian Natural believes the cause of the bitumen emulsion seepage is mechanical failures of wellbores in the vicinity of the impacted locations," it said Wednesday.
The company said it has removed nearly 6,300 barrels of oil from the locations. The site is in a remote wilderness area and some wildlife were reportedly killed from the release.
The company said seepage from steam-injection operations is rare.
An April 2011 spill of 28,000 barrels of oil from an Alberta pipeline was the worst accident of its kind in 30 years.