The dilution effect of N-2/CO2 on the laminar burning velocity of H-2-CO-O-2 mixtures was investigated. The dilution fraction of N-2 and CO2 in the unburned mixtures varied from 0% to 70% and 0%-50%, respectively, and H-2 content in H-2-CO fuels altered from 5% to 100%. All the studies were carried out at standard laboratory conditions (1 atm, 298 K) with equivalence ratio changing from 0.6 to 2.0. The Heat flux method and OH-PLIF (Planar Laser-Induced Fluorescence) based Bunsen flame method were employed to measure the laminar burning velocities. The Li mechanism was used in simulations, due to its good prediction of laminar burning velocities. Based on extensive experimental results, the correlations between dilution fraction and laminar burning velocity reduction rate were analyzed. It was found that, for a given dilution fraction, the reduction in laminar burning velocity is largely independent equivalence ratio and fuel H-2-CO mole fraction. This behavior does not extend to all fuels, e.g. methane. Exploiting the lack of dependence on equivalence ratio and fuel composition, a unified correlation equation was proposed which can be used to predict the laminar burning velocities of H2CO fuels for given fuel component, dilution rate and equivalence ratio. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.