For crude oil, see Petroleum. For other uses, see Oil (disambiguation).

Oil, in a general sense, is a chemical compound that is not miscible with water, and is in a liquid state at ambient temperatures. Such substances are sometimes described as hydrophobic (meaning water hating) or lipophilic (meaning fat loving).

Emulsifiers allow oils and water to mix.

Types

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Hydrocarbons

Certain oils are liquid hydrocarbons or mixtures thereof. They differ from other organic compounds, such as alcohols, ketones and ethers in that they are non-polar. Waxes are chemically similar to this kind of oil, differing only in that they have longer hydrocarbon chains so have stronger intermolecular attractions and are thus solids at room temperature.

Triglycerides

The word oil also refers to triglycerides which are liquids at room temperature, usually in the context of cooking oil. The triglycerides in cooking oil tend to contain unsaturated fatty acid chains (siccative oil), hence the terms monounsaturate and polyunsaturate. Triglycerides found in animals are generally saturated and so tend to be solids at room temperature − if solid, they are called animal fats.

Animal triglycerides are mostly solid while vegetable triglycerides are mostly liquid because animal triglycerides are more saturated. The unsaturation in vegetable triglycerides is in the form of cis alkene groups, which form a kink in the fatty acid chain, preventing neighbouring fatty acid chains from aligning. This effect limits the degree of intermolecular attraction and so allows individual molecules to rotate with respect to each other, the condition for a liquid.

Examples

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Biological

• Vegetable oil, non-volatile oils extracted from plants, usually the seeds
• Essential oil, volatile aromatic oils extracted from plants
• Animal fat, obtained from animal sources

Mineral

• Petroleum or crude oil, a natural resource found in liquid state in the Earth's crust.
• Mineral oil, a by-product of the distillation of petroleum
• Oil shale, a group of sedimentary rocks which may be distilled to obtain petroleum
• Coal oil, distilled from bituminous shale or mineral wax

Synthetic

• Synthetic oil, manufactured from smaller molecules using chemical processes

Applications

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Cooking oil

Edible vegetable and animal oils are frequently used in cooking, due to their ability to reach higher temperatures than water. They also serve as a flavour enhancer and as a supporting medium for vitamins and aromas.

Fuel oil

Oils contain a high amount of stored energy, which can be used for heating and powering combustion engines. Oils used for this purpose are usually derived from petroleum, but biological sources of energy are being evaluated as an alternative to the increasingly expensive crude oil.

Lubrication

Due to their non-polarity, oils do not easily adhere to other substances. This makes them useful as lubricants for various engineering purposes. Suitable oils are often found in the mineral spectrum, as biological oils degrade quickly in most environmental conditions.

Petrochemistry

Petrochemistry is the process of refining crude oil into useful raw materials, plastics, and other oils.

Heat transport

Many oils have higher boiling points than water and lower electrical conductivity, allowing them to be used for liquid cooling systems, especially where electricity is used.

Painting

Color pigments can be easily dissolved in oil, making oil suitable as supporting medium for paints. The slow drying process and miscibility of oil facilitates a realistic style. This method has been used since the 15th century.

Oils

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