A variable geometry swirl combustor, consisting of four concentric annuli was used to examine the effect of combustor geometry variation on pollutant emission. All annuli, except the central one, were equipped with vane-type swirl generators. Natural gas was used as the fuel. Air and fuel were introduced alternatively into the combustor annuli with the central annulus carrying the fuel. Species concentration measurements using gas chromatography, temperature measurements and NO gas analysis were conducted to evaluate the combustor performance. Detailed species and temperature measurements were obtained over a radial distance of 1.5 times the combustor exit radius and up to 2.5 diameters down-stream of the combustor. A total swirl number for the combustor was determined from a theoretical formulation. It is shown here that finer control of the local equivalence ratio and air/fuel mixing may be achieved, yielding optimal combustion efficiencies and low pollutant emission, via variation of the combustor geometry.