With increasing demand for power and with shortages envisioned especially during the peak load times during the summer, there is a need to boost gas turbine power. In Taiwan, most gas turbines operate in combined cycle mode for base load. Only a small portion of gas turbines operates in simple cycle mode for peak load. To prevent the electric shortage due to derating of power plants during hot days, the power augmentation strategies for combined cycles need to be studied in advance. As a solution, our objective is to add an overspray inlet fogging system into an existing gas turbine-based combined cycle power plant (CCPP) to study the effects. Simulation runs were made for adding an overspray inlet fogging system to the CCPP under various ambient conditions. The overspray percentage effects on the CCPP thermodynamic performance are also included in this paper. Results demonstrated that the CCPP net power augmentation depends on the percentage of overspray under site average ambient conditions. This paper also included CCPP performance parametric studies to propose overspray inlet fogging guidelines for combined cycle power augmentation.