Canadian Natural Resources Ltd. reported in May oil was seeping to the surface at locations near the Cold Lake Air Weapons Range in Alberta. The company said the leaks are contained but not stopped.
Company President Steve Laut told The Edmonton Journal he takes full responsibility for the incident.
"We're doing everything we can to see the site cleaned up," he said.
More than 7,000 barrels of oil sands have been removed from four sites. Some of the oil has migrated to a nearby lake, where heavy oil is sinking to the bottom.
Responders deployed oil-containment devices and a special oil-proof fabric at the bottom of the lake to contain the spill.
The company said well failure may have led to the incident. The company was using a steam-injection system to pressurize and warm oil for extraction. The Edmonton Journal said the seep would continue until well pressure abates.
The Alberta Energy Regulator said it was looking into the incident, saying it's too early to make any assessments on the potential mechanical failure.
The company reported Thursday a second-quarter profit of approximately $450 million, a 36 percent decline year-on-year. It said the Alberta incident was not expected to create long-term financial problems.