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) and lipophilic (miscible with other oils, literally). This general definition includes compound classes with otherwise unrelated chemical structures, properties, and uses, including vegetable oils, petrochemical oils, and volatile essential oils. Oil is a nonpolar substance.
The term oil is often used colloquially to refer to petroleum.
is a colloquial term used to refer to certain diverse and unrelated compounds sharing the same physical properties (such as viscosity and a hydrophobic nature), while ignoring related compounds. The compounds found in cooking oil
are chemically very similar, almost identical, to those found in butter and very different from those found in diesel fuel, but while diesel is an oil, butter is not. Indeed diesel is once again very similar to natural gas, but gas is certainly not oil. This disparity stems partly from the fact that oils must be liquid at room temperature, and thus only certain liquid chemicals in many unrelated families are recognised, collectively, as 'oil'. Scientists, instead of using the term 'oil', adopt the terms lipids
and other terms to denote them instead.
Types of oils
All oils, with their high carbon and hydrogen content, can be traced back to organic sources. Mineral oils, found in porous rocks underground, are no exception, as they were originally the 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
and such. These are classified as mineral oils as 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 being 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.
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 to use chemically
, and the scientific term for oils, fats
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.
Many edible vegetable and animal
oils, and also fats
, are used for various in cooking
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 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) and evening primrose oil.
Trans fats, often produced by hydrogenating vegetable oils, are known to be harmful to health.
Almost all oils burn
, which can be used directly, or converted into other forms of fuels by various means. For example, heating water into steam
which is funneled into a turbine
which turns a generator
, which then produces electricity
. Oils are used as fuels
, lighting (e.g. kerosene lamp
), powering combustion
engines, and other purposes. Oils used for this purpose nowadays are usually derived from petroleum
, (fuel oil
, diesel oil
(petrol), etc), though biological oils such as biodiesel
are gaining market share.
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.
can be processed into petroleum
, plastics, and other substances.
has been called oil of vitriol
in pre-scientific times, due to its syrupy consistency. Even in modern times, sulfuric acid 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