The oil that can be extracted from Canadian dirt is either a savior from oil from the unstable Middle East, or an environmental catastrophe in the making.

As Barack Obama prepares to take office in two weeks, the debate is no longer academic. The U.S. president-elect has promised to move forward with an ambitious program to fight climate change.

Not all oil is alike when it comes to environmental repercussions, and many environmentalists single out production from the oil sands as the epitome of "dirty oil." In a recent study, RAND, a policy research group, estimated that oil from the oil sands generated about 10 percent to 30 percent more greenhouse gases than conventional crude.

Canada, in large part because of the production capacity of its oil sands, is now the largest oil supplier to the United States. But environmental groups in both countries are pushing for a slowdown or even a halt to further oil sands development, which is concentrated in northern Alberta.

Operators of oil sands projects and Canadian governments are eager to point to its potential for reducing American dependence on oil from politically unstable regions. Canadian oil sands produce about 1.2 million barrels a day, or about 9 percent of the imported oil consumed in the United States.

Production was headed toward 3.5 million barrels a day by 2015 before the economic slowdown; with the vast reserves available, Canadian oil sands have the potential to produce the equivalent of 1.7 trillion barrels of oil.

The oil sands companies, however, have been scaling back as falling oil prices and the general market turmoil have created a significant economic challenge for the projects.

The entire process adds up to the world's most capital-intensive method for extracting oil. A tiny example: Each of the tires on the cartoonishly oversize dump trucks used in oil sands mining costs about $60,000.

While no one is about to park the giant dump trucks, several companies have recently announced delays in future oil sands investments. In November, a consortium led by Petro-Canada said it would temporarily stop expansions worth 23.8 billion Canadian dollars, or $19.5 billion, of its oil sands operations in Alberta.

"We're not in megaproject mode anymore," Steve Laut, the president and chief executive of Canadian Natural Resources, said to analysts after cutting his company's capital spending plans in half.

And as Washington prepares to deal with climate change, environmentalists, who generally prefer to use the deposits' traditional name - tar sands - are already pressing for restrictions on the projects.