Experimental results and a kinetic modeling were previously reported for the gas phase oxidation of methane in the presence of NO2 at short residence time (20-80 ms) in a microreactor. A detailed kinetic analysis is carried out in the present study in means of flow rate and sensitivity analysis, in order to investigate the role of NO2. A comparison is made of the reaction systems with and without NO2. The concentration profiles of several key species are presented and analyzed in the present study. The CH3O center dot radicals are present in far larger quantities in the CH4/O-2/NO2 system than in the CH4/O-2 system. With NO2, the dominant route to HCHO is through CH3O center dot, primarily involving the reaction: CH3 center dot + NO2 double left right arrow CH3O center dot + NO, followed by: CH3O center dot (+M) double left right arrow CH2O + H center dot (+M) and CH3O center dot + O-2 double left right arrow HO2 center dot + CH2O. The promoting effects of NO2 can be explained by the interconversion NO2/NO, which is mainly related to: HO2 center dot + NO double left right arrow NO2 + OH center dot, NO2 + H center dot double left right arrow NO + OH center dot, NO + CH3O2 center dot double left right arrow CH3O center dot + NO2 and NO2 + CH3 center dot double left right arrow CH3O center dot + NO.