oil

An oil tanker leaving the British Petroleum Hamble terminal near Southampton, England. These huge ships are guided by small pilot boats out of the port and into the busy shipping lanes of the English Channel.

Flammable substance, usually insoluble in water, and composed chiefly of carbon and hydrogen. Oils may be solids (fats and waxes) or liquids. Various plants produce vegetable oils; mineral oils are based on petroleum.

The crude oil (unrefined petroleum) found beneath the Earth's surface is formed from the remains of dead plants and animals. As these plants and animals died they were buried with mud near the sea floor. Over millions of years, heat from the Earth's interior and pressure from overlying rocks slowly changed the dead remains into hydrocarbons (substances containing hydrogen and carbon). The hydrocarbons, being light molecules, moved upwards and became trapped beneath impermeable rocks.

Oil reservoirs are often found beneath the seabed and drilling technology is used to locate these supplies of oil. Crude oil extracted from the ground is refined in fractional distillation columns to produce more useful products such as petrol, diesel, kerosene, plastics, and chemicals for pharmaceuticals.

The three main types of oil are: essential oils, obtained from plants; fixed oils, obtained from animals and plants; and mineral oils, obtained chiefly from the refining of petroleum. Essential oils are volatile liquids that have the odour of their plant source and are used in perfumes, flavouring essences, and aromatherapy. Fixed oils are mixtures of lipids of varying consistency, found in both animals (for example, fish oils) and plants (in nuts and seeds). They are used as foods and lubricants, and in the making of soaps, paints, and varnishes. Mineral oils are composed of a mixture of hydrocarbons, and are used as fuels and lubricants.