Oil

Oil is a smooth liquid (lacking viscosity, slippery to the touch) that does not dissolve in water but dissolves readily in organic solvents such as alcohol and ether. Most oils fall into one of two categories: biological oils derived from plant fruits and animal fats, and mineral oils (hydrocarbons) extracted from beneath the earth.

Oils are generally composed of long molecules of carbon and hydrogen, which is why they do not mix with water. For this reason oils float on water, since their density is typically lower than that of water.

Plant and animal oils

Plant oils are made up of triglycerides—chemical compounds formed from glycerol and three fatty acids. Well-known examples include olive oil, sunflower oil, sesame oil, groundnut oil, and coconut oil. They are used in cooking, soap-making, and also in soap and candle factories. Animal fats such as butter and lard have a similar composition, but typically remain solid at room temperature.

Mineral oils

Crude oil is a hydrocarbon compound extracted from beneath the earth and then refined in processing plants into separate products: petrol, diesel, kerosene, and fuel oil. These oils differ from plant oils in that they contain no fatty acids and therefore cannot be used as food. They are essential as energy sources for vehicles and factories, and are used to make plastics, medicines, and fertilisers.

Essential oils

A third category consists of essential oils, extracted from the leaves, flowers, or stems of plants through distillation. These are not truly oils but rather volatile substances with a characteristic odour. They are used in perfumery, medicinal remedies, and food flavouring.

Use and economy

The oil trade, particularly crude oil, makes up a major part of the global economy, and its price is affected by production levels, political stability, and energy demand. Plant oils, conversely, are among the basic commodities of households and are farmed in many warm climates.