Xylene (from Greek ξύλο, xylo, "wood"), xylol or dimethylbenzene is an aromatic hydrocarbon mixture consisting of a benzene ring with two methyl groups at various substituted positions. The three isomers of xylene have the molecular formula C₈H₁₀, also represented by the semi-structural formula C₆H₄(CH₃)₂. Xylene is a major petrochemical produced by catalytic reforming and also by coal carbonisation in the manufacture of coke fuel. It represents about 0.5–1% of crude oil (depending on the source), and is found in small quantities in gasoline and aircraft fuels. Xylenes are mainly produced as part of the BTX aromatics (benzene, toluene and xylenes) extracted from the product of catalytic reforming known as "reformate". The mixture is a slightly greasy, colorless liquid commonly encountered as a solvent. Xylene was first isolated and named in 1850 by the French chemist Auguste Cahours (1813–1891), having been discovered as a constituent of wood tar. Several million tons are produced annually. In 2011, a global consortium began construction of one of the world’s largest xylene plants in Singapore.