This paper proposes coding, evaluation and selection methodologies for gas turbine systems. The various attributes which characterize the gas turbine systems are identified under different subsystems and different operating characteristics of the gas turbine systems. The attributes include the best load as well as off-base load application and contribute to a generalized gas turbine system rather a typical power generation application or the aircraft applications. A structured approach for coding of the attributes has been proposed in this paper which not only helps in qualitative evaluation of the attributes but also in the feature based selection of the gas turbine system for a set of constraints pertaining to a specific application using TOPSIS. For better qualitative evaluation of the attributes, Graph theoretical methodology has also been adopted for the selection of the gas turbine systems. A comparative evaluation of the techniques adopted in proposed gas turbine systems have also been carried out.