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 (or colloquially tar due to its similar appearance, odour and colour). 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 (320 billion cubic metres). 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 (39.694Ã—109 m3) globally, of which 176.8 billion barrels (28.11Ã—109 m3), or 70.8%, are in Canada.