Petroleum (L. petroleum < Gr. πετρέλαιον lit. "rock oil" was first used in the treatise De re metallica published in 1556 by the German mineralogist Georg Bauer, known as Georgius Agricola.^[1]) is a naturally occurring, flammable liquid found in rock formations in the Earth consisting of a complex mixture of hydrocarbons of various molecular weights, plus other organic compounds.

According to crude oil composition and demand, refineries can produce different shares of petroleum products. Largest share of oil products is used as energy carriers: various grades of fuel oil and gasoline. Refineries also produce other chemicals, some of which are used in chemical processes to produce plastics and other useful materials.

An oil is a substance that is in a viscous liquid state ("oily") at ambient temperatures or slightly warmer, and is both hydrophobic, (immiscible with water, literally "water fearing") and lipophilic (miscible with other oils, literally "fat loving").

In chemistry, an alcohol is any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom of an alkyl or substituted alkyl group. The general formula for a simple acyclic alcohol is C_nH_2n+1OH.