Characteristics

Oil: its Character and Composition

Oil is usually a black, sticky substance used to produce fuel (petroleum), intermediate raw materials (petrochemicals) and materials (plastics). The word petroleum, which means "rock oil," comes from the Greek word petros (rock) and oleum (oil). Oil originates from the organic remains of plants and animals millions of years old. Trapped in fine-grained sediments, the remains were cooked by the heat of the earth to produce oil and gas. Chemically, oil is a complex mixture of organic liquids consisting of carbon, oxygen and hydrogen atoms in different combinations, referred to as hydrocarbons.

How Oil is Formed

Oil comes in many forms. Usually it is black, but green, red or brown oils are not uncommon. When it comes straight out of the ground as a liquid it is called "crude oil" if dark and viscous, and "condensate" if clear and volatile. There two broad types of crude oil. Thin aromatic oils are called "light", whereas thick waxy ones are "heavy." Light oils have an API gravity of 30 to 40 degrees, which means that the density is much less than 1.0 g/cc. These oils float easily on water. By contrast, some heavy oils have an API gravity of less than 12 degrees and are so dense that they sink, rather than float, in water. When solid, oil becomes asphalt, and when semi-solid it becomes tar (or bitumen).

What We Use Oil For

Roughly two-thirds of oil is used for transportation fuels, such as jet fuel, diesel and petrol. Most of the rest heats buildings, generates electricity, or becomes petrochemical products: fertilisers, medicines, cosmetics, plastics, fabrics, synthetic rubber, dyes, adhesives and paint. Oil also provides lubrication for machinery and asphalt for waterproofing and building roads. Many of the items used in our daily lives are made from petroleum feedstocks.