Growing electricity demands within the next century imply an expansion in the current power plant fleet. The achievement of the above, coupled with the need for significant reductions in greenhouse gas (GHG) emissions is a challenging task. Cleaner, more efficient fossil fuel based power plant designs, combined with CO2 capture technologies constitute an attractive option to meet this challenge in the near to medium term. Integrated gasification combined cycle (IGCC) power plants have the lowest carbon dioxide emissions among coal power plants. When combined with a CO2 physical absorption system, substantial GHG emissions reductions can be attained. Depending on the degree of capture, the emissions can match or become less than those of natural gas fired combined cycle (NGCC) power plants. This paper is a technical and economic comparison of the performance of five plant designs in the 500 MW output range: IGCC without CO2 capture, IGCC with 80% capture, IGCC with CO2 emissions equal to those of a NGCC, IGCC with CO2 and H2S co-capture, and NGCC without capture. ASPEN Plus (TM) models of the above plants were developed and the following plant performance results are discussed: net power output, efficiency, plant ancillary energy requirements and overall CO2 emissions. Economic evaluations for all cases are presented, including the cost methodology and economic basis. The capital investment, cost of electricity and carbon dioxide mitigation costs for all plants are detailed and compared. The simulation results show that the economics favour higher capture levels in new IGCC plants. The CO2 mitigation costs corresponding to IGCC plants with 80% capture are slightly lower than those corresponding to IGCC plants with equal emissions to those of NGCC plants (28 vs. 30 US$/tonne CO2 avoided). The capital cost difference (per kW of net installed capacity) between the above plants is 7%, while the CO2 emissions of the former are almost half those of the latter. IGCC plants with CO2 and H2S co-capture have substantial technoeconomic advantages over IGCC plants that capture CO2 and H2S separately. Based on a 577 MW IGCC, the power output decreases only to 552 MW for the co-capture case, whereas it drops to 488 MW when CO2 and H2S are captured separately. The incremental capital cost of co-capture plants is 6%, and their electricity production cost increase is less than half a cent, with respect to an IGCC without capture. The CO2 mitigation cost of co-capture plants is at least four times lower than their separate CO2 and H2S capture counterparts. (c) 2005 Elsevier Ltd. All rights reserved.