Humid air injection offers improved plant operational flexibility. If additional power can be sold, the engine can be operated at increased power with improved heat rate; increasing both electric power and fuel consumption. If additional power cannot be sold, the engine can be operated at the same power (as without air injection) but with improved heat rate; this saves fuel while maintaining power production. If the plant operates with a given quantity of fuel, the engine can be operated at increased power while burning the same fuel quantity as without air injection. Finally, the minimum operating power of the gas turbine may be reduced allowing the engine to burn less fuel when the spark spread is negative, but it is desirable to run the engine.