The role of CO2 on the moist oxidation of CO in the CO-NO and CO-NO2 systems is analyzed from both experimental and modelling points of view, under flow reactor conditions, at atmospheric pressure, over the temperature range of 700-1400 K and at fuel-rich (lambda = 0.5) and fuel-lean (lambda = 2) environments. Sensitivity and reaction rate analyses were used to identify the role of CO2 in this process. Additionally, the effect of the presence of NO and NO2 on CO oxidation is considered. Results indicate significant differences in combustion characteristics between CO oxidation in a 0% or 25% CO2 atmosphere, in the presence of both NO or NO2. In particular, at high temperatures, either NO or NO2 promote the CO oxidation in CO2 atmosphere, through a specific NO-NO2 interconversion system, which is catalysed by the CO2 presence. However, in the 1075-1150 K range and independent of the CO2 atmosphere, the CO oxidation is strongly inhibited by NO2 presence. The effect of CO2 and NOx presence on CO conversion is quite similar for both O-2 levels.