Nov. 30--FORT MCMURRAY, Alberta -- Energy security is not for the fainthearted.

In the giant, open-pit mines north of this sub-Arctic boomtown, oil literally is carved out of the ground. Shovels the size of buildings scoop hundreds of tons of oil-soaked dirt into Caterpillar dump trucks as big as two-story houses. The trucks move to and from the pits in a perpetual storm of dust.

Everything in the Canadian oil sands -- from the machinery to the seemingly infinite oil reserves -- is extra large.

"This is mining to the max -- it's very extreme," said Brian Patey, who came from Newfoundland in eastern Canada and now runs the truck shop at the Albian Sands Energy mine, a joint venture by oil companies Shell, Chevron and Marathon. Patey said that when he first saw a mine truck, "I thought it was the biggest thing in the world."

Once shunned by oil companies that preferred easier-to-exploit reservoirs of liquid crude, Alberta's oil sands now have made Canada the top foreign supplier of crude to the U.S. They contain the world's second-largest storehouse of crude -- surpassing U.S. reserves by a factor of eight.

If the United States is to reduce its reliance on importing oil from countries that are unfriendly or unstable, Canada's oil sands are the place.

Yet, no other source of oil better illustrates our society's Faustian dilemma between energy security and environmental responsibility.

Extracting the tarlike oil called bitumen and converting it into the light crude that refiners want is an energy-intensive process that annually produces as much carbon dioxide as 6 million cars.

Put another way, extracting oil from the sands creates about three times the greenhouse gases as conventional drilling.

Canada, which in 1997 signed the Kyoto treaty on reducing emissions, now struggles to reconcile its newfound role of energy superpower with its promise to cut greenhouse gases. Some say oil-sands profits have cooled the country's enthusiasm for the treaty.

"It's the one thing that is really dragging us in the opposite direction from Kyoto targets," said Simon Dyer, a fellow with the Pembina Institute, a Canadian environmental think tank.

Some U.S. policymakers question whether this country should continue to increase its reliance on the oil sands, due to their heavy environmental footprint.

And President-elect Obama could add pressure on the oil-sands industry to clean up its act, said Chris Sands, a senior fellow with the Hudson Institute think tank in Washington, D.C.

"For Obama, fossil fuels are something we should be moving away from -- the dirtier, the worse," Sands said.

Extreme mining

Northern Alberta reeks of oil. Over millions of years, vast quantities of petroleum were trapped in beachlike sand formations spanning an area roughly the size of Florida.

In some places, oil lies so close to the surface that it seeps out of the earth, a black, viscous goop that sometimes naturally spills into lakes and the Athabasca River, which flows northward toward the Arctic.

Shallow deposits of this very thick oil -- called bitumen -- are mined in open quarries, much like iron ore. Most of the oil, though, lies in deeper deposits commonly exploited by injecting steam into the ground to heat and liquefy the bitumen so that it can be pumped out.

The smell of petroleum begins just a few miles north of Fort McMurray, where both sides of the highway are lined with mazes of tubes and tall cylinders called "upgraders." That's where the bitumen is processed into synthetic light crude, the type most valuable to refiners because it's easy to convert into gasoline.

When the highway reaches the Albian Sands mine, a 4.5-square-mile trench carved out of the boreal forest, it's the landscape that smells. The mine's giant trucks can haul up to 380 tons of dirt, yielding about 190 barrels of oil, or about 3,600 gallons of gasoline -- enough to fuel the average Washington state car for nine years.

The dug-up moonscape of the mine looks like an outlandish, 70-yard-deep sandbox for giants. Stand still too long, and your shoes will sink a little in the oily muck.

"We're a vast dirt-moving operation," Shell spokeswoman Janet Annesley said.

This rich region is about 700 miles north of the U.S. border, but most of the 1.2 million barrels of oil extracted here daily goes to the Midwest and even Texas, providing about 9 percent of U.S. crude imports. Washington state's refineries receive at least 10 percent of their oil from Alberta, a figure expected to increase as production wanes on Alaska's North Slope.

Albian Sands, one of three active mines in the region, produces about 155,000 barrels of bitumen a day; an expansion under way will mean an additional 100,000.