An IGCC (integrated gasification combined cycle) plant consists of a power block and a gasifier block, and a smooth integration of these two parts is important. This work has analyzed the influences of the major design options on the performance of an IGCC plant. These options include the method of integrating a gas turbine with an air separation unit and the degree of nitrogen supply from the ASU to the gas turbine combustor. Research focus was given to the effect of each option on the gas turbine operating condition along with plant performance. Initially, an analysis adopting an existing gas turbine without any modifications of its components was performed to examine the influence of two design options on the operability of the gas turbine and performance of the entire IGCC plant. It is shown that a high integration degree, where much of the air required at the air separation unit is supplied by the gas turbine compressor, can be a better option considering both the system performance and operation limitation of the gas turbine. The nitrogen supply enhances system performance, but a high supply ratio can only be acceptable in high integration degree designs. Secondly, the modifications of gas turbine components to resume the operating surge margin, such as increasing the maximum compressor pressure ratio by adding a couple of stages and increasing turbine swallowing capacity, were simulated and their effects on system performance were examined. Modification can be a good option when a low integration degree is to be adopted, as it provides a considerable power increase. (C) 2008 Elsevier Ltd. All rights reserved.