The effect of NO and SO 2 on the oxidation of a CO-H 2 mixture was studied in a jet-stirred reactor at atmospheric pressure and for various equivalence ratios (0.1, 1, and 2) and initial concentrations of NO and SO 2 (0-5000 ppm). The experiments were performed at fixed residence time and variable temperature ranging from 800 to 1400 K. Additional experiments were conducted in a laminar flow reactor on the effect of SO 2 on CO-H 2 oxidation in the same temperature range for stoichiometric and reducing conditions. It was demonstrated that in fuel-lean conditions, the addition of NO increases the oxidation of the CO-H 2 mixture below 1000 K and has no significant effect at higher temperatures, whereas the addition of SO 2 has a small inhibiting effect. Under stoichiometric and fuel-rich conditions, both NO and SO 2 inhibit the oxidation of the CO-H 2 mixture. The results show that a CO-H 2 mixture has a limited NO reduction potential in the investigated temperature range and rule out a significant conversion of HNO to NH through reactions like HNO + CO ⇔ NH + CO 2 or HNO + H 2 ⇔ NH + H 2 O. The chain terminating effect of SO 2 under stoichiometric and reducing conditions was found to be much more pronounced than previously reported under flow reactor conditions and the present results support a high rate constant for the H + SO 2 + M ⇔ HOSO + M reaction. The reactor experiments were used to validate a comprehensive kinetic reaction mechanism also used to simulate the reduction of NO by natural gas blends and pure C 1 to C 4 hydrocarbons.