Recent environmental assessments, including the RAND study, also do not further the cause of the oil sands industry. While climate change is the current focus, it is not the only environmental issue surrounding the projects.

Spent water used in oil sands projects is placed in lake-size tailings ponds, one of which killed about 500 migrating birds in April. Seepage from the ponds is polluting rivers in northern Canada, some scientists argue. In December, Environmental Defence, an environmental lobby group based in Toronto, estimated that about four billion liters of contaminated water leaked from the ponds each year. (The Alberta government and the oil industry dispute that finding.)

Strip mining of the oil sands, the most common method of extraction, has destroyed large swaths of boreal forest, an important habitat for migratory birds and other wildlife. In December, a study published by the Natural Resources Defense Council and two other groups found that six million to 166 million birds could be lost over the next 30 to 50 years because of that disruption.

Producers say they are making efforts to address environmental concerns. Mr. Laut’s company, which recently completed a 110,000-barrel-a-day oil sands project, is developing systems to capture and store much of the carbon dioxide it emits. It has applied for government grants to test a system that will trap some of its carbon dioxide output by bubbling the exhaust gases from an upgrading plant through the spent water from a strip mine’s steam.

Large-scale programs to capture and store carbon dioxide are not yet in place. The demonstration project of Canadian Natural Resources, for example, is not scheduled to begin until 2010.

With oil prices around $49 a barrel, profitability is fast eroding at oil sands projects and may already be vanishing at some operations. Producers have widely differing cost structures and varying definitions of profitability. But Andrew J. Leach, a professor of environmental economics at the University of Alberta in Edmonton, estimates that long-established plants can operate with prices as low as $30 a barrel. But he said newer operations need $60 to $70 a barrel for acceptable returns, and no one will proceed with proposed projects until prices return to the $80 to $90 range.

Exactly how Canada could participate in the shaping of an American strategy for climate change is unclear.