Abstract: A method of augmenting power in a gas turbine plant that includes a compressor, at least one combustor, a turbine component and an output shaft, comprising a) supplying air and water to a heat recovery boiler; b) providing a turbine controller that controls supply of air, steam or a mixture of air and steam to the combustor; c) storing data in the turbine controller including properties of air, steam and equations for determining properties of any mixture of air and steam; d) measuring a differential pressure of the air, steam or mixture of air and steam across a metering tube located upstream of the combustor; e) determining instantaneously the mass flow rate of the air, steam or mixture of air and steam as a function of said differential pressure and desired power output; and f) supplying the air, steam or mixture of air and steam to the combustor at the flow rate determined in step e); wherein step f) is carried out with a control valve downstream of the metering tube, the control valve operatively connect