Results from investigating the effectiveness of using a power turbine equipped with variable guide vanes are presented. Control ranges of turbines using these guide vanes are determined in the most typical operating modes of gas-turbine engines and units for thermal power-engineering purposes and gas transportation systems. Recommendations are formulated for the expediency of using the variable guide vanes of a power turbine to improve the operational efficiency of gas-turbine engines and units during the cold period of the year under partial-load conditions and in some other cases.