used. A 2008 estimate set the total world resources of oil shale at 689 gigatones—equivalent to yield of of shale oil, with the largest reserves in the United States, which is thought to have , though only a part of it is recoverable. According to the 2010 World Energy Outlook by the International Energy Agency, the world oil shale resources may be equivalent of more than of oil in place of which more than may be technically recoverable. A 2016 conservative estimate by the World Energy Council set the total world resources of oil shale equivalent to yield of . For comparison, at the same time the world's proven oil reserves are estimated to be . Geographical allocation There is no comprehensive overview of oil shale geographical allocation around the world. Around 600 known oil shale deposits are diversely spread throughout the earth, and are found on every continent with the possible exception of Antarctica, which has not yet been explored for oil shale. Oil shale resources can be concentrated in a large confined deposit such as the Green River formations, which were formed by a large inland lake. These can be many meters thick but limited by the size of the original lake. They may also resemble the deposits found along the eastern American seaboard, which were the product of a shallow sea, in that they may be quite thin but laterally expansive, covering thousands of square kilometers. The table below reports reserves by estimated amount of shale oil. Shale oil refers to synthetic oil obtained by heating organic material (kerogen) contained in oil shale to a temperature which will separate it into oil, combustible gas, and the residual carbon that remains in the spent shale. All figures are presented in barrels and metric tons. Africa Major oil shale deposits are located in the Democratic Republic of Congo (equal to 14.31 billion metric tons of shale oil) and Morocco (12.3 billion metric tons or 8.16 billion metric tons of shale oil). Deposits in Congo are not properly explored yet. In Morocco, oil shale deposits have been identified at ten localities with the largest deposits in Tarfaya and Timahdite. Although reserves in Tarfaya and Timahdit are well explored, the commercial exploitation has not started yet and only a limited program of laboratory and pilot-plant research has been undertaken. There are also oil shale reserves in Egypt, South Africa, Madagascar, and