In a search for potential methods of reducing future air transport fuel consumption, advanced conventional turbofan and more unconventional propulsion systems were examined. Early results encouraged a more detailed evaluation of an advanced Brayton cycle gas generator in a turbofan engine or geared to an advanced multi-bladed, small diameter propeller. The fuel savings potential and operating costs are estimated for the turbofan and turboprop systems to assess both the energy conservation possibilities and the airline economic benefits.