This paper is a case study of thermodynamic and economics related analyses applied to an existing gas/steam combined cycle cogeneration plant. Basic thermodynamic properties of the plant are determined by energy analysis utilizing main operation conditions. Exergy destruction and losses within the plant are investigated to determine thermodynamic inefficiencies in the system and to assist for guiding future improvements in the plant. Cost bakances are applied to several subsystems in the plant, hence cost formation in the plant is observed. Besides, cost of each product of the system is calculated.