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Oil sands are an unconventional source of oil, consisting principally of a mixture of sand, clay, water and a dense, viscous form of petroleum known as bitumen. In fact, "bituminous sands" is the more technically correct name for this resource, although "oil sands" has become, through usage, the more commonly used term.
Only recently have oil sands been considered an economically viable part of the world's petroleum reserves. With the increase in oil prices starting in 2007, it has become profitable to extract bitumen from the oil sands mixture, then upgrade, transport, and refine it into usable products.
Oil sands are found in various parts of the world, but the largest deposits are in Alberta, Canada, comprising approximately 70% of the world reserve. Significant deposits are also found in Kazakhstan and Russia.