To provide more insight into the laminar burning velocity reduction of diluted syngas premixed flames, the laminar burning velocities of diluted syngas premixed (H-2/CO/N-2/air and H-2/CO/CO2/air) laminar spherical flames were systematically and thoroughly investigated experimentally via Schlieren technology. In the present investigation, the volume fraction of H-2 was varied from 30% to 70%, the volume fraction of CO was varied from 30% to 70%, the volume fraction of CO2 was varied from 0% to 60%, and the equivalence ratio was varied from 0.7 to 1.0. In the present investigation, the effects of equivalence ratio, hydrogen fraction, and dilution fraction on the laminar burning velocities were studied. Compared to N-2 dilution, the laminar burning velocity reduction with CO2 dilution was analysed through the thermal, transport, and, chemical effects. In addition, the contributions of third-body and direction effects were also studied. (C) 2016 Elsevier Ltd. All rights reserved.