The reformate gas enriched counterflow lean premixed CH4/air flames were studied by numerical simulation in this paper. The reformate gas was assumed to be the product of partial oxidation of methane by air, and it consists of H2, CO and N2. Detailed chemistry and complex thermal and transport properties were employed. The results indicate that the addition of the reformate gas enlarges the flammable region, and extends the lean flammability limit of counterflow CH4/air premixed combustion. When the reformate gas is added, the formation of NO is reduced in a near-stoichiometric flame, and increased in an ultra-lean flame at a constant equivalence ratio. The more significant advantage of the reformate gas enriched lean premixed combustion is that it greatly reduces the formation of NO by allowing a combustor to operate at leaner condition without any effect on flammable range. Further, the addition of the reformate gas decreases the formation of NO2 and N2O at a constant equivalence ratio. ; peer reviewed: ; NRC Pub: Yes ; system details: machine converted author identifier PE to PID, February 2012