This study investigates the combustion performance of synthetic gas that is composed of hydrogen, carbon monoxide, nitrogen, carbon dioxide and steam, and evaluates the dilution effect of the last three gases. Combustion tests of a model GE7EA industrial gas turbine are conducted at ambient pressure and the air inlet temperature of 380 degrees C. NOx and CO emissions, combustion instabilities, flame shapes, and the temperature at several points of the combustion chamber are observed while varying the dilution ratio of nitrogen, carbon dioxide and steam. NOx emissions are decreased as the amount of diluents is increased, and the reduction of NOx emission per unit power generation is logarithmically related only to the diluent's heat capacity which is the product of mass flow rate of diluent and constant pressure heat capacity. In most of the tested cases, the combustion efficiency is satisfactorily good in that CO is emitted below 10 ppm, and neither flash back nor combustion instability is observed. From the results, we report that nitrogen, carbon dioxide and/or steam are applicable to a syngas turbine to control NOx emission with ensuring reliable operation. (C) 2012 Elsevier Ltd. All rights reserved.