The present study represents an effort to correlate the dependence of NOx emissions on heat losses to the atmospheric environment in a CH4/air fueled combustor. To this end, the numerical analysis was performed over a wide range of residence times, equivalence ratios and heat losses using a perfectly stirred reactor (PSR) code. The numerical results showed that the calculated NOx concentration initially increased, reached a maximum value and then decreased with increasing residence time when the heat loss was present. The similar variation was observed in changes in the thermal NO concentration that was evaluated by only considering the reactions associated with the thermal (Zeldovich) NO mechanism. With the heat loss increased, the calculated NOx concentration was substantially reduced for all equivalence ratios investigated. In addition, the reductions in the NOx concentration with respect to residence time became faster with increasing the equivalence ratio particularly for fuel rich conditions. The observed variations in the calculated NOx concentration over the residence time (NOx/tau) were found to fit well to the following correlation: ln(NOx/tau) = a(HLI) + b. In the correlation, HLI is the dimensionless heat loss parameter and coefficients a and b are constants expressed as a function of adiabatic flame temperature (for a given equivalence ratio) and equivalence ratio, respectively. (C) 2010 Elsevier Ltd. All rights reserved.