US President Barack Obama has signaled that Canada's oil sands industry should not be granted an exemption from strict regulations to limit emissions of greenhouse gases.

His stance could add to the already high costs of developing this vast resource which is increasingly regarded as one of North America's most secure sources of energy.

Obama travels to Canada on Thursday for his first foreign visit as head of state. During his campaign for the presidency he pledged to fight global warming through implementation of a carbon tax or creation of a carbon emissions market.

Energy will be one of the main topics of discussion between Canadian Prime Minister Stephen Harper and Obama. Harper is expected to urge the US president not to impose strict environmental regulations on high-carbon sources of energy like oil sands and coal, because it could make them unprofitable to produce.

"What we know is that oil sands create a big carbon footprint," Obama said in a television interview with the Canadian Broadcasting Corporation Tuesday. "I think that it is possible for us to create a set of clean energy mechanisms that allow us to use things not just like oil sands, but also coal. The United States is the Saudi Arabia of coal, but we have our own homegrown problems in terms of dealing with a cheap energy source that creates a big carbon footprint."

Canada is the biggest foreign supplier of oil to the US, and in recent years a growing share of that oil has been derived from the oil sands region of northern Alberta which are estimated to hold a massive 173 billion barrels of oil.

About 780,000 barrels of oil per day are produced from the Alberta oil sands and exported to the US. Canada currently sells about 60% of its oil sands output to US refiners.

Converting the bitumen extracted from the oil sands into gasoline and diesel fuel takes about 20% percent more energy -- and generates a correspondingly larger amount of carbon emissions -- than using conventional crude.

With that in mind, environmentalists on both sides of the border have been calling on Obama to honor his past pledges to rein in carbon emissions.

"He doesn't come out and say there will be a dispensation," said David Biette, director of the Canada Institute in Washington. "He seems to put all energy sources into the same arena."

During the CBC interview, Obama called on Canada and the US to invest more in advanced technology that could capture carbon and store it underground.

"All of us are going to have to work together in an effective way to figure out how we balance the imperatives of economic growth with very real concerns about the effect we're having on our planet," Obama said. "And ultimately I think this can be solved by technology."

The White House and Democratic leaders in Congress are pushing aggressively to pass legislation that would either impose a carbon tax on fuels or create a carbon trading system that would cap US carbon emissions.

Either approach would increase the cost of producing oil from the Alberta oil sands, which is mined from the earth as bitumen or heated and pumped to the surface. The higher greenhouse gas emissions associated with the oil sands are caused in large part by the energy used to separate the oil out from the sand and other impurities.

The recent steep fall in oil prices to current levels of around $40 a barrel have already had a big impact on plans to expand Canadian oil sands production.

Canadian bank TD Newcrest calculates that around 600,000 b/d of new output, originally scheduled to come on stream by 2010 or 2011, has been postponed.

Bill Murray, Washington

For comprehensive coverage and analysis of US energy policy, visit Energy Intelligence's special web portal, Obama Energy Vision, at www.energyintel.com/obama.