The electric field gradient (EFG) components at the oxygen nucleus in CO, OCS, HNCO, H2CO, H2O, C2H4O, and O-2 were calculated in fully optimized ab initio geometries for a wide variety of correlated and uncorrelated methods employing small and extended Gaussian basis sets. Within a specific type of theory and fixed basis level, the calculated EFG components are found to be accurately proportional to quadrupole coupling constants which are accurately known from microwave studies. We determine the characteristic proportionality constant, slightly different for each level of theory, which corresponds to a "calibrated" oxygen-17 quadrupole moment Q that is optimal for theoretical EFG calculations at the chosen level of theory. This generalizes a calibration method due to Huber, offering an improved procedure for determining absolute quadrupole moments (by extrapolating calibrated values to higher levels of theory) without the need for experimental structural data. More importantly, this procedure allows quadrupole coupling properties of quite reasonable accuracy to be obtained, even from very modest levels of theory (e.g., HF/3-21G), despite current uncertainties in the experimental oxygen-17 quadrupole moment.