Fuel oil (also known as heavy oil, marine fuel, bunker, furnace oil, or gasoil) is a fraction obtained from the distillation of petroleum (crude oil). It includes distillates (the lighter fractions) and residues (the heavier fractions).
The term fuel oil generally includes any liquid fuel that is burned in a furnace or boiler to generate heat, or used in an engine to generate power. However, it does not usually include other liquid oils, such as those with a flash point of approximately 42 °C (108 °F),[why?] or oils burned in cotton- or wool-wick burners. In a stricter sense, fuel oil refers only to the heaviest commercial fuels that crude oil can yield, that is, those fuels heavier than gasoline (petrol) and naphtha.
Fuel oil consists of long chain hydrocarbons, particularly alkanes, cycloalkanes, and aromatics. Small molecules, such as those in propane, naphtha, gasoline, and kerosene, have relatively low boiling points, and are removed at the start of the fractional distillation process.
Heavier petroleum derived oils like diesel fuel and lubricating oil are much less volatile and distill out more slowly.
Oil has many uses; it heats homes and businesses and fuels trucks, ships, and some cars. A small amount of electricity is produced by diesel, but it is more polluting and more expensive than natural gas. It is often used as a backup fuel for peaking power plants in case the supply of natural gas is interrupted or as the main fuel for small electrical generators
