The gauge-independent atomic orbital (GIAO) approach is used within the coupled Hartree-Fock (CHF) approximation to compute the oxygen NMR shielding constant in the carbonyl group for a series of molecules. We apply a correction to account for the correlation effects which is based on the comparison with the experimental results for a few molecules. Our final results enable us to predict the oxygen shielding or interpret the results of the experiment, in particular when the experimental data for the gas phase are not known.