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, literally "water fearing") and lipophilic (miscible with other oils, literally "fat loving"). 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.
Types of oils
All oils, with their high carbon and hydrogen content, can be traced back to organic sources or space.  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, gasoline, diesel 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 bitumen or tar, 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, 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
Almost all oils burn in air generating heat, which can be used directly, or converted into other forms of fuels by various means. For example, heating water into steam which is funnelled into a turbine which turns a generator, which then produces electricity. Oils are used as fuels for heating, 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 (gasoline), etc), though biological oils such as biodiesel are gaining market share.
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.
But in some application Bio-oil is used for applications like hydraulic systems as an oil leak would have disastrous consequences for the environment. The 'Environment Agency' stipulate that machines working on some projects next to sensitive water courses and lakes use Bio-oil, to reduce the risk if leaks occur.
based on wiki article for this glossary item
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