The cost effective R&D strategy is required especially for large-scale technologies because their development demands a large amount of investment in general. A mixed integer programming model was developed for the optimum technology development strategy in the field of energy systems. The module of the technology development process in the model is based on GERT (Graphical Evaluation and Review Technique). In the module, a target technology is broken down into many elemental technologies. Usually several target technologies are involved for the evaluation of technology development strategy of one field and some of the elemental technologies are used common to a number of target technologies. Since elemental technologies are explicitly modeled, their spillover effects are necessarily evaluated in this model analysis. The proposed method was applied to the evaluation of the development strategy of four types of IGCC (Integrated coal Gasification Combined Cycle) technologies which have different levels of thermal efficiencies. The total investment on both their R&D and practical use is optimized under the constraint of meeting a certain exogenous scenario of electricity demand. The evaluation results include the optimum additional investment allocation among the developments of various elemental technologies; developments of integration technology for IGCC-43%, IGCC-55% and IGCC-48%, coal gasification technology, oxide dispersion strengthened superalloy technology for the gas turbine blade and vane, ceramic matrix composite technology for the gas turbine blade, dry sulfur-removal technology, etc. are cost-effective. (C) 2004 Elsevier Ltd. All rights reserved.