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General structure of a triglyceride, the main constituent of vegetable oil and animal fats
Synthetic motor oil being poured

An oil is any substance that is in a viscous liquid state ("oily") at ambient temperatures or slightly warmer, and is both hydrophobic (immiscible with water) and lipophilic (miscible with other oils, literally). Oils have a high carbon and hydrogen content and are nonpolar substances. The general definition above includes compound classes with otherwise unrelated chemical structures, properties and uses, including vegetable oils, petrochemical oils, and volatile essential oils. All oils can be traced back to organic sources.

The term "oil" is often used colloquially to refer to petroleum.



Mineral oils

Mineral oils, found in porous rocks underground, originated from organic material, such as dead plankton, accumulated on the seafloor in geologically ancient times. Through various geochemical processes this material was converted to mineral oil, or petroleum, and its components, such as kerosene, paraffin waxes, gasoline, diesel and such. These are classified as mineral oils because they do not have an organic origin on human timescales, and are instead derived from underground geologic locations, ranging from rocks, to underground traps, to sands.

Other oily substances can also be found in the environment; the most well-known of those is asphalt, occurring naturally underground or, where there are leaks, in tar pits.

Petroleum and other mineral oils (specifically labelled as petrochemicals), have become such a crucial resource to human civilization in modern times they are often referred to by the ubiquitous term of "oil" itself.

Organic oils

Oils are also produced by plants, animals and other organisms through organic processes, and these oils are remarkable in their diversity. Oil is a somewhat vague term in chemistry; instead the scientific term for oils, fats, waxes, cholesterol and other oily substances found in living things and their secretions, is lipids.

Lipids, ranging from waxes to steroids, are somewhat hard to characterize, and are united in a group almost solely based on the fact that they all repel, or refuse to dissolve, in water, and are however comfortably miscible in other liquid lipids. They also have a high carbon and hydrogen content, and are considerably lacking in oxygen compared to other organic compounds and minerals.


A bottle of olive oil used in food.


Many edible plant and animal oils and fats are used in cooking and food preparation. In particular, many foods are fried in oil much hotter than boiling water. Oils are also used for flavoring and for modifying the texture of some foods e.g. Stir Fry.

Health advantages are claimed for a number of specific oils such as omega 3 oils (fish oil, flaxseed oil, etc), evening primrose oil and olive oil. Trans fats, often produced by hydrogenating vegetable oils, are known to be harmful to health.


Almost all oils burn in aerosol form generating heat, which can be used directly, or converted into other forms of fuels by various means. The oil that is pumped from the ground, is then shipped via oil tanker to an oil refinery. There, it is converted from crude oil to any form of gasoline, diesel fuel, kerosene and heating oil.

Electricity generation

Oil and any of its more refined products are often used to create electricity. This is done by means of a steam engine. The steam engine turns the thermal energy into rotary motion, which can then be transformed into electricity, by means of a generator.

Heat transport

Many oils have higher boiling points than water and are electrical insulators, making them useful for liquid cooling systems, especially where electricity is used.


Due to their non-polarity, oils do not easily adhere to other substances. This makes oils useful as lubricants for various engineering purposes. Mineral oils are more suitable than biological oils, which degrade rapidly in most environmental conditions.


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.


Crude oil can be processed into petroleum, plastics, and other substances.

Other uses

Sulfuric acid has been called oil of vitriol in pre-scientific times, due to its viscous consistency. Even in modern times, it is sometimes called vitriolic acid, and caustic personalities are called "vitriolic". Sulfuric acid is not a petrochemical, and in modern parlance, is not an oil.


Oils have been used throughout history as a fragrant or religious medium. Oil is often seen as a spiritually purifying agent. It is used in religious ceremonies, such as the chrism used in baptism, and has traditionally been used to anoint kings and queens. Oil that is associated with one or more saints is known as "oil of saints" and believed by some to have beneficial properties, as is "oil of martyrs"[1].

See also

  • Abiogenic petroleum origin
  • Emulsifier, allow oils and water to mix
  • List of countries by oil production
  • List of countries by oil consumption
  • List of countries by oil proven reserves
  • List of countries by oil exports
  • List of countries by oil imports
  • Oil pollution
  • Peak oil
  • The End of Oil
  • Wax, compounds with oil-like properties that are solid at common temperature
  • Petroleum


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