Shale oil is an unconventional oil produced from oil shale rock fragments by pyrolysis, hydrogenation, or thermal dissolution. These processes convert the organic matter within the rock (kerogen) into synthetic oil and gas. The resulting oil can be used immediately as a fuel or upgraded to meet refinery feedstock specifications by adding hydrogen and removing impurities such as sulfur and nitrogen. The refined products can be used for the same purposes as those derived from crude oil. The term "shale oil" is also used for crude oil produced from shales of other unconventional, very low permeability formations. However, to reduce the risk of confusion of shale oil produced from oil shale with crude oil in oil-bearing shales, the term "tight oil" is preferred for the latter. The International Energy Agency recommends to use the term "light tight oil" and World Energy Resources 2013 report by the World Energy Council uses the term "tight oil" for crude oil in oil-bearing shales. History Oil shale was one of the first sources of mineral oil used by humans. In the 10th century, the Arabic physician Masawaih al-Mardini (Mesue the Younger) first described a method of extracting oil from "some kind of bituminous shale". It was also reported to have been used in Switzerland and Austria in the early 14th century. In 1596, the personal physician of Frederick I, Duke of Württemberg wrote of its healing properties. Shale oil was used to light the streets of Modena, Italy at the turn of the 18th century. The British Crown granted a patent in 1694 to three persons who had "found a way to extract and make great quantities of pitch, tarr and oyle out of a sort of stone." Later sold as Betton's British Oil, the distilled product was said to have been "tried by diverse persons in Aches and Pains with much benefit." Modern shale oil extraction industries were established in France during the 1830s and in Scotland during the 1840s. The oil was used as fuel, as a lubricant and lamp oil; the Industrial Revolution had created additional demand for lighting. It served as a substitute for the increasingly scarce and expensive whale oil. During the late 19th century, shale-oil extraction plants were built in Australia, Brazil and the United States. China, Estonia, New Zealand, South Africa, Spain, Sweden and Switzerland produced shale oil in the early 20th century. The discovery of crude