Abstract: An internal combustion engine and method of operation is disclosed as having a combustion chamber design which allows for staged combustion within the chambers. The internal combustion engine of the invention is designed as a split chamber, staged combustion engine which comprises a cylinder and having at least two regions formed therein. Within the cylinder is a piston slidably disposed therein to form a plurality of combustion chambers in association with the cylinder, and particularly at least one primary and secondary combustion chamber which are communicable with one another. Fuel delivery is accomplished by fuel injectors or the like associated with the primary combustion chamber, being operable to admit fuel into the primary combustion chamber at preselected intervals and in predetermined amounts. The fuel admitted in top the primary combustion chamber is ignited to begin initial combustion of the fuel as a first stage of combustion.