One of the main challenges of restructured power systems is to maintain sufficient installed generation capacity to meet system demand in different load points of transmission network both for present and future time. This paper presents a comprehensive Generation Expansion Planning (GEP) scheme in pool market, ensuring secure operation of power system in different load points. The proposed algorithm is divided into two programming levels: master and slave. In the master level, a Modified Game Theory (MGT) is proposed to evaluate the contrast of generation companies (GENCOs) by Independent System Operator (ISO). Besides that, the reliability level of all load points is optimized based on the availability of the composite power system, i.e. generation and transmission level. In the slave level, a Dynamic Programming (DP) method is used to find the best solution of each GENCO for decision making of investment. The validity of the proposed GEP is studied on Roy Billinton Test System (RBTS). (C) 2011 Elsevier Ltd. All rights reserved.