Oil


 * For other uses, see Oil (disambiguation).

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, 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.

Food oils
Several edible vegetable and animal oils, and also fats, are used for various purposes in cooking and food preparation. In particular, many foods are fried in oil much hotter than boiling water. Oils are also used for flavouring 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.

Oil as fuel
Most oils burn in air generating heat which can be used directly or converted into other forms of energy in the usual ways. 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 also used.

Environmental concerns
Petroleum is a nonrenewable resource, and burning it produces carbon dioxide, a greenhouse gas. Biological oils are renewable and do not produce net carbon dioxide, but require land to grow. Both also produce pollutants such as NOx.

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

Manufacture of petrochemicals
Crude oil can be processed into plastics and other substances. See Petrochemistry.

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.

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.

Religion
Oils have been used throughout history as a fragrant or religious medium. Oil is often seen as a spiritually purifying agent, for example Chrism.

Massage
Oil allows massage strokes to glide along the skin. The oil is selected based on the viscosity for the type of massage being conducted. A relatively high-viscosity oil such as almond oil may be used for a luxuriant, slow style, while a lighter oil such as grape seed oil may be selected for a more athletic or rapid approach. Scent may be added.