Gasoline

Gasoline is not a single substance but a mixture of hundreds of chemicals refined from crude oil. Crude oil consists of many hydrocarbons, from light substances like natural gas to heavy ones like asphalt. These hydrocarbons are separated into various groups during refining, and then some of these groups are remixed (reformulated) for automotive gasoline.

Hydrocarbons consist only of hydrogen and carbon atoms. They are classified in three families - aromatics, olefins, or paraffins - according to their molecular structure. Each oil company mixes these hydrocarbons according to its own formulas.

Additives - including oxygenated fuels - are blended with hydrocarbons to help the overall product perform better. To assure a common standard of quality, various industry-wide specifications have been established.

The two most important standards as related to vehicle performance are octane and volatility.