An experimental study was carried out to determine the nitrogen oxides emission characteristics with oxygen depletion as some of the pollutant generation rates were heavily dependent upon oxygen depletion. The emission rates of NO and NO_2 as well as NO_x were determined quantitatively on kerosene fired space heaters. The NO_x emission characteristics of kerosene heaters were classified as two emission models, the one represented the conventional radiant-convective models of which the emission rate decreased proportionally with oxygen depletion, the other expressed the fan-heater models which had two distinct oxygen phases. The first phase occurs in the sharp decline from the initial oxygen point of K_0 to a certain oxygen point of Kc. The second phase occurs in the decline beyond the point of Kc.