Crude oil in its natural state has very few practical uses. However, when it is separated into its component parts by the process of fractionation, or refining, those parts have an almost unlimited number of applications.

In the first 60 years after the process of petroleum refining was invented, the most important fraction produced was kerosene, widely used as a home heating product. The petroleum fraction slightly lighter than kerosene — gasoline — was regarded as a waste product and discarded. Not until the 1920s, when the automobile became popular in the United States, did manufacturers find any significant use for gasoline. From then on, however, the importance of gasoline has increased with automobile use.

The term gasoline refers to a complex mixture of liquid hydrocarbons that condense in a fractionating tower at temperatures between 100° and 400°F (40° and 205°C). The hydrocarbons in this mixture are primarily single- and double-bonded compounds containing...