The two kinds of conventional fuels in use today are gasoline and diesel. Other kinds of fuels, like CNG and LPG, are classified as alternative fuels.

In the last 30 years, pollution control experts around the world have come to realize that cleaner fuels is a critical component of an effective clean air strategy.

In recent years, this understanding has grown, deepened, and spread to most regions of the world. Fuel quality is now seen as not only necessary to reduce or eliminate certain pollutants directly, but also as a precondition for the introduction of many important pollution control technologies.