USA President Barack Obama said Tuesday Canada's massive oil sands operations leave a big carbon foot print and he compared it America's coal industry.

In advance of his first foreign trip, Obama expressed concern about the environmental impact of the oil sands in an interview with the Canadian Broadcasting Corp. in Washington.

Obama heads to Canada on Thursday. Canadian Prime Minister Stephen Harper has said energy security and the environmental impact of Alberta's massive oil sands operations will be priorities during the meeting. Harper is expected to lobby Obama on the merits of the oil sands as a safe and secure source of oil.

Industry officials estimate northern Alberta could yield as much as 175 billion barrels of oil, making Canada second only to Saudi Arabia in crude oil reserves.

But critics say the growing operations by major oil companies will increase greenhouse gas emissions and threaten Alberta's rivers and forests. Experts say producing a barrel of oil from sand results in emissions three times greater than a conventional barrel of oil.