Terms used in the compressed natural gas fuel business to indicate the speed at which different systems are capable of fueling vehicles. A fast-fill CNG dispenser, such as might be used in a retail fueling station, can generally fuel a passenger car in 5 to 7 minutes.

On the other hand, at fleet facilities such as school bus garages, slow-fill systems are often used. Slow-fill fueling typically requires several hours and is usually done overnight.

The term slow-fill is also used in connection with the filling of tank vehicles. The slow-fill technique is employed to reduce generation of static electricity.

See also Switch loading.