Critical assessment was performed for a type of oxy-fuel integrated coal gasification combined cycles (IGCC) that was comprised of proven components. A type of two-stage entrained-flow gasifier consisting of combustor and reductor sections was simulated by a one-dimensional model that has been proven through application to gasifiers of industrial scales. It was successfully reproduced on Aspen Plus (R) and integrated together with the other components into a commercial-scale IGCC system. The oxidizing agents were not only O-2 and CO2 (carrier gas for conveying the coal) but also additional CO2 or CO2/H2O, that was required to suppress hydrocarbons formation and maintain the combustor temperature allowing molten ash to have sufficiently low viscosity. The net thermal efficiency was predicted as a function of steam/coal mass ratio (S/C) within a range of 0-0.4. Increasing S/C up to 0.2 increased the cold gas efficiency slightly but resulted in decrease in the net thermal efficiency of the system. This was mainly due to the extraction of steam from the high pressure steam turbine exhaust, causing loss of power output. Resulting in lower cold gas efficiency due to higher oxygen ratio, higher moisture content of the pulverized coal gave higher net thermal efficiency due to less steam consumption for coal drying. The net efficiency was optimized at approximately 39% on a higher-heating-value basis without steam feeding, which was higher by 6-7 points than that for conventional IGCC with oxygen-blown gasification combined with CO2 recovery.