As oil has become scarcer and more expensive, oil companies have begun seriously pursuing a politically charged method of oil extraction in Canada.

The ­world's second-­largest oil reserve lies under Alberta in the form of oil sand, which must be processed extensively to yield bitumen, a hydrocarbon mixture related to asphalt that can be turned into crude oil. It is estimated that 174 billion barrels of oil of varying quality could be recovered from the sands. Development is speeding ahead: so far, 34 billion Canadian dollars have been spent developing the oil sands, and another 45 billion in development projects will be completed by 2010 by companies including Petro-Canada, Syncrude, and Suncor.

Oil companies use large machinery and pipelines to transport the sand and rely on welling technologies to extend their reach to the bitumen buried far below the surface. With production at about one million barrels of oil per day in 2005 and expected to double by 2010, environmental groups worry that oil-sands development is speeding ahead too quickly. The following photos illustrate the process--and impact--of getting oil from sand.