Abstract: A system for simultaneously increasing combustion efficiency and reducing pollutant emissions. Oxygen enriched air (i.e., air from which a portion of the nitrogen has been removed so that the oxygen concentration is higher than in normal air) and water droplets of predetermined size are both present in the cylinder of a four cycle internal combustion engine during the power/combustion stroke. Oxygen enriched air may be mixed with normal air drawn into the combustion chamber during the intake stroke. Also, and alternatively, the droplets may be water or H.sub.2 O.sub.2 bubbles filled with normal or oxygen-enriched air.