Coal oil is a shale oil obtained from the destructive distillation of cannel coal, mineral wax, or bituminous shale, once used widely for illumination.

Chemically similar to the more refined, petroleum-derived kerosene, it consists mainly of several hydrocarbons of the alkane series, with 10 to 16 carbon atoms in each molecule and a higher boiling point (175–325 °C) than gasoline or the petroleum ethers and lower than the oils.

The term was in use by the late 18th century for oil produced as a byproduct of the production of coal gas and coal tar.  In the early 19th century it was discovered that coal oil distilled from cannel coal could be used in lamps as an illuminant, although the early coal oil burned with a smokey flame, so that it was used only for outdoor lamps; cleaner-burning whale oil was used in indoor lamps

In the United States, coal oil was widely manufactured in the 1850s under the trade name Kerosene, manufactured by a process invented by Canadian geologist Abraham Gesner. James Young won his patent lawsuit against the Gesner process in the United States in 1860. But by that time, US coal oil distillers were switching over to refining cheaper petroleum, after the discovery of abundant petroleum in western Pennsylvania in 1859, and oil from coal operations ceased in the US.

Coal oil was once used as an internal and topical home remedy as a general cure-all for many ailments, including coughs, flu, cuts, abrasions, and wounds. Internal applications were administered by adding this toxic petroleum product to sugar cubes, molasses, honey or some other substance to mask the taste, while topical applications were applied adding to bandages or by pouring the coal oil directly on the affected area.

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