Constant-volume combustion experiments measuring laminar burning velocity are presented for combinations of methane, inert diluent and H-2/CO mixtures that would result from steam reforming of methane. The experiments illustrate the very attractive prospects of on-board steam reforming in natural gas powered vehicles that would employ exhaust gas recirculation (EGR) to improve combustion performance and reduce NOx emissions. Laminar burning velocity in the partially reformed fuel stream can be maintained at levels similar to that of air/natural gas mixtures by increasing the prereforming of the fuel at increasing concentrations of EGR. Up to 40% dilution was tested, requiring that 53% of the methane fuel be reformed to maintain burning velocity. Calculations indicate NOx levels are similar to scenarios with unreformed fuel. The knowledge base from this and similar experiments is required to allow for the future adoption of on-board fuel reforming in IC engines. This is a critical intermediate step in introducing hydrogen as a fuel to the currently fossil-hydrocarbon oriented economy and fuel delivery infrastructure. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.