The status of the Mod III kinematic Stirling engine (155 hp at 2800 rpm) is reviewed with emphasis on natural gas emissions test results and manufacturing cost predictions. Laboratory emissions results are presented for an existing upgraded Mod I (UM-I) engine that has volumetric firing rates comparable to the Mod III. Stirling emissions levels are compared with several internal combustion (IC) engines. Preliminary vehicular emissions measurements with natural gas were also obtained from an UM-I engine installed in a Dodge D-150 pickup truck.Cost for commercial manufacture of the Mod III is determined on the basis of a value-engineered design. This analysis indicated that manufacture of engines in sufficient volume to satisfy projected market needs for a stationary application would provide an adequate manufacturing base to produce the engine at a commercially competitive price.