Canadian refiner Suncor Energy said it started a four-week maintenance period at its facility in Montreal, which can process 137,000 barrels of oil per day.

Suncor said about 900 of its employees would be involved in planned maintenance activity at its Montreal refinery.

"The planned maintenance is designed to support safe, reliable operation of the refinery," the company said in a Monday statement. "During this period Suncor has made the necessary arrangements to ensure sufficient finished products are available and expects all customer supply agreements will be met."

Suncor's facility in Montreal processes oil into gasoline, heavy fuel oil, and other petroleum products.

In early April, the company said it plans to spend about eight weeks overhauling its oil sands refinery in Edmonton, Alberta. It's designed to process 142,000 barrels of oil sands per day into light oils.

Suncor operates three refineries in Canada and one in the United States with a combined processing capacity of 462,000 bpd.