a fuel supply system for a gaseous fuel operated vehicle engine in which a compressed gas from a bomb is decompressed by regulator means and then mixed with air to supply air - fuel mixture to the engine . the regulator means is divided into at least two units , locating an upstream regulator and the bomb in a luggage room section of a vehicle , and locating a downstream regulator and a mixer in an engine room section of the vehicle . a low pressure piping system is extended across a passenger &# 39 ; s room section of the vehicle for interconnecting the upstream and downstream regulators . particular structures of the regulator are also disclosed for effectively preventing freezing of fuel gas components which would lead to constriction of a high pressure gas passage formed in the regulator .