Abstract: A multiple phase fuel supply system for an internal combustion engine includes a pressurized supply tank for holding liquid hydrocarbon fuel having the characteristic that it is normally a vapor at room temperature and atmospheric pressure. At least one liquid injector receives liquid fuel from the tank and injects the liquid in the intake system of the engine, and at least one vapor injector receives fuel vapor from the tank and injects the vapor into the intake system of the engine. A controller operates the liquid and vapor injector such that at least one operating parameter of the fuel supply tank will be maintained between predetermined limits.