Abstract: An internal combustion engine with greatly reduced emission of pollutants includes a piston having a piston chamber communicating through orifices with the working chamber of the cylinder and an annular balancing chamber communicating with the working chamber through balancing slots when the piston is between 20.degree. to 30.degree. from its bottom center position. Breathing holes are provided at the opposite end of the balancing chamber. Air from the balancing chamber flows into the working chamber in response to the vacuum therein during the intake stroke, flows from the working chamber into the piston chamber during the compression stroke, and from the piston chamber into the working chamber during the power stroke to stratify the combustion process and inhibit the emission of hydrocarbon and carbon monoxide pollutants. Some exhaust gases are admitted to the balancing chamber during the exhaust stroke to be readmitted to the working chamber during the next intake stroke.