Jet fuel A-1. Jet fuel designed for use in aircraft powered by gas-turbine engines. It is clear to straw-colored in appearance. The most commonly used fuels for commercial aviation are Jet A and Jet A-1 are produced to a standardized international specification. Jet fuel is a mixture of a large number of different hydrocarbons. The range of their sizes is restricted by the requirements for the product, for example, the freezing point or smoke point. Kerosene-type jet fuel has a carbon number distribution between about 8 and 16 carbon numbers (carbon atoms per molecule); wide-cut or naphtha-type jet fuel (including Jet B), between about 5 and 15 carbon number.