This paper discusses the fundamentals of a new concept for an internal combustion engine which operates according to an hybrid thermodynamic cycle between the well known Otto cycle and the Atkinson cycle; thus this new engine is referred here as the Otto-Atkinson engine. The objective of this engine is to provide an improved performance characteristic in fuel consumption as well as in pollution control. An important feature of this Otto-Atkinson engine is that it enables these objectives to be relatively easily incorporated into the conventional piston type Otto engine, requiring no new technology. Preliminary experimental results comparing the performance of the Otto engine with three experimental set-ups of the Otto-Atkinson engine operating at the same load and speed are included. It was found that fuel consumption of the Otto-Atkinson engine was up to 19% lower, and that the CO and NOx were lower than in the conventional engine.