Military and commercial turbofan STOL transport work at the Douglas Aircraft Company during the past four years has led to the consideration of commonality between the USAF Medium STOL Transport and a short-range, medium-sized commercial STOL transport.General requirements for the two airplanes appear to be similar and include a cruise speed of Mach 0.75-0.80 for a 500-nautical mile range after takeoff from a 2000-foot airstrip. Both require a wide body; and the payload, furnishings, and equipment yield comparable STOL takeoff weights. Both can be designed with a high wing, a moderate wing loading, and the same STOL lifting concept. A common engine size appears feasible, and basic engine characteristics such as bypass ratio need not be different.Results of a preliminary commonality study are presented in which several cases with varying degrees of commonality are evaluated in terms of costs. The cost benefits of shared development and production were found to outweigh the penalties related to design compromises, resulting in lower costs for both military and commercial operators.