An optimal planning for gas turbine cogeneration system was applied to find whether or not the adoption of the system to an office building or hotel in Seoul, Korea is profitable. The planning problem considered in this study is to determine the optimal configuration of the system equipments and optimal operational policy of the system when the annual energy demands of electric power, heat and cooling are given a priori. The optimal configuration of the system equipments has been determined based on annual cost method with proper choice of representative energy demand patterns obtained for the building and hotel in a 1-year period. A mixed-integer linear programming and the branch and bound algorithm have been used to obtain the optimal solution. The planning method employed here may be applied to making decision on the adoption of the cogeneration plant to any specific office building or hotel. (c) 2006 Elsevier Ltd. All rights reserved.