The reaction between NsO and CO was studied in a single-plus shock tube over the temperature range 1320°-2280°K, in mixtures of the reactants highly diluted with Ar. In the range of temperatures 1317°-1908°K the rate constant for the bimolecular reaction, N2O+CO→N 2+CO2, was found to be k1= 1.1×10 exp(-23000/RT) cm mole-1-sec-1. From the rates of formation of CO2 above 1642°K, a constant for the nonradiative third-order recombination of O and CO was obtained (for the temperature range 1500°-3000°K), O+CO+Ar-CO2+Ar, s=2.8×10 eip(+23800/Ar) cmmol-sec-1. The large negative activation energy so deduced is shown to be in full agreement with the low value for the activation energy previously observed for CO2 decomposition. An energy diagram was constructed on the basis of a recent CO flame study and results on the limiting high-pressure CO2 decomposition. The mechanisms for the radiative and the three-body recombination, and the dissociation of CO2, are discussed in terms of this energy diagram.