The influence of the main operating conditions in the reburning zone using natural gas on the NO, HCN, and NH3 concentrations obtained at the exit of this zone has been analyzed. Experiments with a wider range of variable values than those presented in the literature have been performed. The variables analyzed have been the temperature (1200-1500 degrees C), the natural gas concentration (1-4.5%) or reburning fuel fraction (0.08-0.50), the oxygen concentration at the inlet of the reburning zone (0-5%), the stoichiometric ratio in the reburning zone (0.75-1.05), the primary NO concentration (100-1200 ppm), and the gas residence time (94-280 ms).