We report the characteristics of heat transfer and emissions in natural gas fired flameless oxidation conditions created using multiple semi-industrial regenerative burners. Burner positions and firing modes (parallel and staggered) are varied, and their effects on efficiency, emissions (NO, CO) and temperature uniformity are studied. Also the excess air ratio and the cycle time have been varied. The operation uses two burner pairs together to provide 200 kWth giving a volumetric heat release closely resembling real industrial operating conditions (48 MW/m(3)). The parallel mode operation shows better results concerning low emission of CO and NO, and uniform temperature distribution in the furnace. On the other hand, the staggered mode operation showed a comparatively low performance due to a developed unsymmetrical flow pattern in the furnace. Single digit NO emission was measured for the parallel mode with low CO concentration due to low and uniform temperature. CO concentration is strongly dependent on the burner cycle time because the switching of burners generates periods of unstable and non-uniform flow pattern and also temperature distribution temporarily. The numerical simulation with skeletal reaction showed typical reaction characteristics of flameless oxidation, which is a slow and uniform reaction progress in the furnace. Meanwhile, the reaction model needs to improve its accuracy because the reaction speed appears to be slower than the experiment, and the simulation of a case showed extinguished reaction. The comparable simulation results also showed an order higher CO emission and an order lower NO emission, which is assumed to be related with low reaction kinetics. (C) 2013 Elsevier Ltd. All rights reserved.