The aim of this part of ISO 15403 is to provide manufacturers, vehicle operators, fuelling station operators and others involved in the compressed-natural-gas vehicle industry with information on the fuel quality for natural gas vehicles (NGVs) required to develop and operate compressed-natural-gas vehicle equipment successfully. Fuel meeting the requirements of this part of ISO 15403 should a) provide for the safe operation of the vehicle and associated equipment needed for its fuelling and maintenance; b) protect the fuel system from the detrimental effects of corrosion, poisoning, and liquid or solid deposition; c) provide satisfactory vehicle performance under any and all conditions of climate and driving demands. Some aspects of this part of ISO 15403 may also be applicable for the use of natural gas in stationary combustion engines.