Fuel/air mixing effects in a premixer have been examined to investigate the combustion characteristics, such as the emission of NO(x) and CO, under simulated lean premixed gas turbine combustor conditions at normal and elevated pressures of up to 3.5 bar with air preheat temperature of 450 K. The results obtained have been compared with a diffusion flame type gas turbine combustor for emission characteristics. The results show that the NO(x) emission is profoundly affected by the mixing between fuel and air in the combustor. NO(x) emission is lowered by supplying uniform fuel/air gas mixture to the combustor and the NO(x) emission reduces with decrease in residence time of the hot gases in the combustor. The NO(x) emission level of the lean premixed combustor is a strong function of equivalence ratio and the dependency is smaller for a traditional diffusion flame combustor under the examined experimental conditions. Furthermore, the recirculation flow, affected by dome angle of combustor, reduces the high temperature reaction zone or hot spot in the combustor, thus reducing the NO(x) emission levels. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.