Abstract This work explores the effect of O 2 addition on CO 2 dissociation and on the vibrational kinetics of CO 2 and CO under various non-equilibrium plasma conditions. A self-consistent model, previously validated for pure CO 2 discharges, is further extended by adding the vibrational kinetics of CO, including electron impact excitation and de-excitation (e-V), vibration-to-translation relaxation (V-T) and vibration-to-vibration energy exchange (V-V) processes. The vibrational kinetics considered include levels up to v = 10 for CO and up to v 1 = 2 and v 2 = v 3 = 5, respectively for the symmetric stretch, bending and asymmetric stretch modes of CO 2 , and accounts for e-V, V-T in collisions between CO, CO 2 and O 2 molecules and O atoms and V-V processes involving all possible transfers involving CO 2 and CO molecules. The kinetic scheme is validated by comparing the model predictions with recent experimental data measured in a DC glow discharge ignited in pure CO 2 and CO 2 –O 2 , operating at pressures in the range 0.4–5 Torr (53.33–666.66 Pa). The experimental results show a lower vibrational temperature of the different modes of CO 2 and a decreased dissociation fraction of CO 2 when O 2 is added to the plasma but an increase of the vibrational temperature of CO. On the one hand, the simulations suggest that the former effect is the result of the stronger V-T energy-transfer collisions with O atoms which leads to an increase of the relaxation of the CO 2 vibrational modes. On the other hand, two main mechanisms contribute to the lower CO 2 dissociation fraction with increased O 2 content in the mixture: the back reaction, CO(a 3 Π r ) + O 2 → CO 2 + O and the recombinative detachment O − + CO → e + CO 2 .