The Orbital Engine is a new internal combustion engine displacer. Development of a 7 chamber 3.5 litre Otto cycle version has shown that it is approximately one third the size and weight of similar displacement conventional powerplants, can be perfectly balanced, and features an inherent combustion chamber gas motion which is the basis for a new and efficient combustion process. Development has overcome mechanical and gas sealing problems and the fuel consumption and emissions results presented compare favourably with other engines. When fully developed the engine will offer large fuel economy gains in automotive applications due to its light weight, small size and efficient combustion.