The operating envelope of a direct fired solid oxide fuel cell gas turbine (SOFC/GT) hybrid was determined using a hardware-based simulation facility designed and built by the U.S. Department of Energy, National Energy Technology Laboratory (NETL). Three methods of cathode airflow management using bypass valves in a hybrid power system were evaluated over the maximum range of operation. The cathode air flow was varied over the full range of operation of each bypass valve incremented independently. Each operating point was taken at a steady state condition and was matched to the thermal output of a corresponding fuel cell operation. Turbine electric load was also varied so that the maximum range of fuel cell operation could be studied. Results are presented depicting the operating envelope in terms of cathode air flow, fuel cell load, turbine load, and compressor surge margin.