Abstract: An electrolysis cell is provided for use in connection with a combustion engine, for generating hydrogen and oxygen gases which are added to the fuel delivery system as a supplement to the gasoline or other hydrocarbons burned therein. The hazard of explosion of the mixture of generated gases is eliminated by withdrawing the gases through a connection with the vacuum line of the positive crankcase ventilation (PCV) system of the engine and by utilizing a slip-fitted top cap for the electrolysis cell, which cooperates with the PCV vacuum line to prevent explosive containment of generated gases in case of accident. Use of the generated gases as a fuel supplement enables substantial increases in fuel efficiency, while at the same time reducing the emission of pollutants.