We have measured O 1s photoelectron angular distributions in coincidence with the O+-CO+ fragment ion pairs of CO2 molecules at the photoelectron energies of 90, 120 and 150 eV. The observed molecular frame photoelectron angular distributions are left-right asymmetric as a consequence of an enhancement in bond-breaking probability for the CO bond involving the O atom with the 1s hole, compared with the other CO bond. Comparison of the experimental data with the calculations due to our semi-empirical model enables us to deduce the value of 1.4 for this enhancement in the relative bond breaking probability. (C) 2014 Elsevier B.V. All rights reserved.