The available experimental and theoretical information on gaseous actinide oxides covering both the neutral and the ionic species are reviewed. The ground-state electronic structures of the oxides of An = Th-Cm have been obtained by the well-tested SOCASPT2 method, and therefore they are very likely reliable. The ground electronic states of the oxides of An = Bk-Lr were reported only from B3LYP calculations. The reliability of B3LYP for this molecular property has been demonstrated by the agreement with the SO-CASPT2 results for almost all of the neutral and ionic oxides for An = Th-Cm. Some additional data with proper quality could be obtained on the basis of empirical relationships evaluated from the computed geometries and vibrational frequencies, reliable knowledge of either parameter can enable confident prediction of the other. The compilations are very helpful in both interpreting complex experimental results and for predicting molecular data not available from experiment.