A 5.8 liter rotary engine was converted to natural gas from a liquid fueled, stratified-charge model. Changes to the engine for natural gas operation include provision for multiple spark plug locations in the rotor housing, a rotor with a trailing flat-top pocket and a 9.6 compression ratio, and dual side intake ports. The engine is initially rated at 185 kW (250 BHP) per rotor and 3600 RPM.A single rotor version of the engine was dynamometer tested. Test results, including fuel consumption and exhaust emissions data, are discussed. The testing included multiple spark plugs, a range of spark plug positions and spark timing, and a wide range of air-fuel ratios. The engine was able to operate at very lean air- fuel ratios without incidence of misfire. Low NOx emissions were achieved within practical operational parameters.With increasingly stringent exhaust emissions regulations in the future, there has been a renewed interest in natural gas engines. By operating at very lean air-fuel ratios, emissions of oxides of nitrogen (NOx) from natural gas engines can potentially be reduced to meet these regulations. This paper is a report of initial efforts in the development of a natural gas rotary engine which would be able to meet future exhaust emissions regulations.The specific objectives of the activity reported here were to design a test engine capable of demonstrating performance of a moderately large rotary engine operating with natural gas fuel, and to enable testing of a range of parameters for the purpose of evaluating and selecting features advantageous to gas engine performance in terms of both fuel consumption and exhaust emissions. The result would be to demonstrate predicted power output, a reasonable fuel economy for an initial trial as the basis for future improvement, and to demonstrate the expected low exhaust emissions, particularly NOx. Due to previously observed characteristics of rotary engines, it was believed that a rotary engine could be produced that would provide low exhaust emissions, particularly low NOx, concurrent with acceptable fuel economy. Development and demonstration of satisfactory performance with the single-rotor test engine would provide the basis for production of a family of multi-rotor engines having the same advantageous features. The resulting engines would be capable of significant continuous power rating, from 375 kW (500 HP) to 932 kW (1250 BHP), in two to five rotor form at the initial projected rating.