The potential performance of optimized gas-steam combined cycles built around latest-generation gas turbine engines is analyzed, by means of energy/exergy balances. The options here considered are the reheat gas turbine and the H-series with closed-loop steam blade cooling. Simulations of performance were run using a well-tested Modular Code developed at the Department of Energy Engineering of Florence and subsequently improved to include the calculation of exergy destruction of all types (heat transfer, friction, mixing, and chemical irreversibilities). The blade cooling process is analyzed in detail as it is recognized to be of capital importance for performance optimization. The distributions of the relative exergy destruction for the two solutions—both capable of achieving energy/exergy efficiencies in the range of 60 percent—are compared and the potential for improvement is discussed. [S0742-4795(00)00902-9]