Competition in liberalized energy markets and increasing environmental concerns call for industrial power generation that is both cost effective and environmentally friendly. This is true for both the operation of existing as well as the development of new energy systems. Meeting this challenge requires new, more powerful tools able to deal simultaneously not only with the tecnical complexity of such systems but with their economic and environmental characteristics as well. Project OPTIGAZ centers on the development of such a tool for the design of combined cycle plants and their associated gas pipeline networks. This article outlines the principal concepts underlying the methodological basis for this tool and provides some preliminary results to illustrate its application to the synthesis, design and operation of energy systems.