Abstract: A fuel system for and a method of operating an internal combustion engine wherein an aqueous solution of hydrogen peroxide is injected into the combustion chamber after a conventional fuel and combustion gas mix (i.e. gasoline-air) has been ignited. The hydrogen peroxide and water charge supplies additional oxygen to insure complete combustion of the hydrocarbon fuel and simultaneously the high energy content present in the hydrogen peroxide serves to boost the power output of the engine. Furthermore, the water in the hydrogen peroxide charge produces a washing effect on the engine combustion chamber which enables combustion to proceed at a lowered temperature which results in lowered NO.sub.x content of the exhaust gas. The more complete fuel combustion brought about by this system also eliminates the need for catalytic converters.