The amount of NOx produced during combustion is computationally investigated for methane, Russian-Shebelinka, Iran-South Pars, and Turkey-Tekirdag natural gases in different operating conditions. The flames are laminar and stoichiometric premixed. The chemical kinetic mechanism used in the study consists of 59 reactions and 25 chemical species. A computer program (CREK) is used to compute mole and mass fractions of products. The highest and the lowest NOx amounts are obtained during methane-air and Turkey-Tekirdag natural gas-air combustions. Amounts of methane and nitrogen in the compositions of natural gases affect the amount of NOx produced during combustion. The amount of NOx increases with increasing reactant inlet temperature. Increased reactant total mass amount raises the amount of NOx, but it causes mass fraction of NOx to decrease in the products. Increasing humidity ratio of the burning air reduces the amount of NOx.