Abstract: A unique process is disclosed for modifying an automobile engine to improve fuel economy and reduce harmful exhaust emissions by introducing water and an oxidizing agent, such as hydrogen peroxide, when the engine is under load. The carburetor of a standard engine is adjusted to provide a very lean air-fuel mixture and to increase the air-fuel ratio substantially (e.g., 10 to 20 percent). The amount of hydrogen peroxide injected into the engine depends on the rate of fuel flow and may be regulated by the throttle valve or intake manifold pressure. Means are provided for maintaining a supply of hydrogen peroxide including a high pressure mixing tank containing water and hydrogen peroxide and a pair of removable oxygen tanks for a continuous supply of oxygen to the tank.