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Strict regulations of NO x emission standards have resulted in an optimized performance of combustion chambers. The present paper describes the effects of burned gas recirculation on NO x emissions from hythane−oxygen flames in a separated jet burner. Burners with separated fuel and oxidizer jets permit a high dilution of reactants and a large recirculation zone of burned gases in the combustion chamber, which favors the decrease of nitrogen oxide emissions. In this study, the oxyfuel burner was equipped with two nozzles: the first nozzle supplied a hythane flow (a mixture of natural gas and hydrogen), and the second nozzle supplied pure oxygen. The hydrogen content in the fuel varied from 0 to 20% in volume. The influence of the distance between the nozzles (12−100 mm) and the global equivalence ratio of the mixture was analyzed. Measurements of combustion product concentrations were carried out at the combustion chamber exit using a water-cooled probe and a NO x analyzer. The velocity fields and the size of the recirculation zone were determined by the particle image velocimetry (PIV) technique in the reacting flow. The results showed that an increase in the size of the recirculation zone leads to a decrease in NO x emissions (up to 96%) and that NO x emissions are inversely proportional to the measured surface area of the burned gas recirculation zone. Because of the reaction between recirculated CO 2 and thermal NO and its chemical effects, NO x emissions decrease in lean combustion because of the destruction of NO.