Abstract: A six-stroke internal combustion engine with reciprocating pistons wherein the six strokes are the admission of air, the first compression accompanied or followed by a possible cooling, a second compression followed by a combustion, the first expansion producing a usable work, the second expansion producing also a usable work and finally the discharge of the combustion gases, this engine, whose combustion is either with spark-ignition (gasoline version) or with auto-ignition (diesel version), will include preferably a multiple of five non-uniform cylinders, and will have an energy efficiency of up to 30% higher than that of a four-stroke internal combustion engine.