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Oil sands, tar sands or, more technically, bituminous sands, are a type of unconventional petroleum deposit. The oil sands are loose sand or partially consolidated sandstone containing naturally occurring mixtures of sand, clay, and water, saturated with a dense and extremely viscous form of petroleum technically referred to as bitumen. Natural bitumen deposits are reported in many countries, but in particular are found in extremely large quantities in Canada. Other large reserves are located in Kazakhstan and Russia. The estimated worldwide deposits are more than 2 trillion barrels. The estimates include deposits that have not yet been discovered; proven reserves of bitumen contain approximately 100 billion barrels. Total natural bitumen reserves are estimated at 249.67 billion barrels globally, of which 176.8 billion barrels, or 70.8%, are in Canada. Oil sands reserves have only recently been considered to be part of the world's oil reserves, as higher oil prices and new technology enable profitable extraction and processing. Oil produced from bitumen sands is often referred to as unconventional oil or crude bitumen, to distinguish it from liquid hydrocarbons produced from traditional oil wells. (via Freebase)