Plant Design Expert (PDE), a knowledge-based power plant design system, can be used to design plants for maximum performance and efficiency. PDE creates inputs to GT PRO, a widely used software program for combined-cycle and cogeneration plant designs. It runs the GT PRO computational module and presents the resulting cycle as graphic and text outputs. A PDE user simply enters site conditions and constraints, power and process steam requirements, and ecomonic tradeoff between cost and efficiency. PDE offers a choice of potential system designs which meet the stated criteria, then creates a detailed cycle heat balance design.