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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.
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Hydrocarbons
Certain oils are liquid hydrocarbons or mixtures thereof. Hydrocarbons are long carbon and hydrogen chains known as alkanes or alkenes depending upon bond orientation. 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, resulting in a greater number of intermolecular attractions per molecule, and are thus solids at room temperature.
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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, 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.
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Biological
Vegetable oil, non-volatile oils extracted from plants, usually the seeds
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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
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Synthetic
Synthetic oil, manufactured from smaller molecules using chemical processes
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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 large amount of stored energy, which can be converted by burning into other forms of energy. Fuel oil is used for heating, lighting (c.f. kerosene lamp) 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 suspended in oil, making it 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.
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