Figure 6. Historical trend in trade-off between performance and fuel economy, segregated by car size (average for U.S. new-car fleet, 1975–1995).

Aviation fuel is the fuel used to power aircraft in flight. It must satisfy the unique requirements of both the engine and the airframe of the aircraft. Currently the great majority (more than 99%) of aviation fuel used in both civil and military aircraft is jet fuel. A small quantity of aviation gasoline is still used in small aircraft. Early aircraft used motor gasoline to power their spark ignition engines because the aviation and auto worlds shared the same early engines. In recognition of aviation's more stringent requirements compared to ground transportation, separate specifications for aviation gasoline were developed after World War I. Subsequent aircraft spark ignition engine developments as World War II approached identified the need for high octane in aviation fuel for improved performance...