This paper presents a comprehensive optimal expansion planning model for an integrated generation and transmission system. The objective function used in the optimization model comprises of the capital cost of the new generating units to be built, the fuel cost incurred in running all the generating units in the system including the transportation cost of fuel from the fuel source ends to the generating unit locations and the capital cost of the new transmission lines to be installed for meeting the forecasted system demand at the target planning year. Constraints taken care of in the model include the fuel availability limits at the fuel sources, the fuel transportation limits for the transportation of fuels from fuel sources to the generating unit locations, capacity of generating units required to be built as well as the power transmission limits of the transmission lines in the system. The developed model is tested on a system to bring out the relative advantage of adopting the integrated generation and transmission expansion planning approach as compared to the sequential approach of first planning the generation expansion and then the transmission expansion. The model has also been applied to the integrated generation and transmission expansion planning of a real system. (C) 2012 Elsevier Ltd. All rights reserved.