Aviation jet fuel is petroleum based fuel, or petroleum and synthetic fuel blend, used to power aircraft. They have more stringent requirements than fuels used for ground use, such as heating and road transport, and contain additives to enhance or maintain properties important to fuel performance or handling. It is designed for use in aircraft powered by gas–turbine engines. It is colorless to straw-colored in appearance. The most commonly used fuels for commercial aviation are Jet A and Jet A–1, which are produced to a standardized international specification. The only other jet fuel commonly used in civilian turbine engine powered aviation is Jet B, which is used for its enhanced cold weather performance.