The motivation of this study is to explore the feasibility of extending the EGR (exhaust gas recirculation) diluent tolerance for methanellair mixtures with reformer gas (CO and H-2). A preheated cylindrical combustion chamber was used to measure the laminar burning velocity of methane/air mixture with variations of EGR diluent, reformer gas, temperature and pressure. The experiments were carried out at the range of initial temperature from 298 K to 498 K and initial pressure from 1 atm to 5 atm. The maximum EGR fraction is 40%. Reformer gas was introduced to raise the burning velocity of methane/EGR mixture to the undiluted level. Results indicate that the reformer gas has potential to improve the burning velocity while reducing the nitric oxide emission. (c) 2006 Elsevier Ltd. All rights reserved.