Ionization potentials (IPs) for MO3 and MO2 for M = U, Mo, W, and Nd have been predicted using the Feller-Peterson-Dixon (FPD) approach at the coupled cluster CCSD(T)/complete basis set level including additional corrections. The additional corrections are mostly small, with spin-orbit effects contributing less than 0.05 eV, except for NdO2 where the correction lowers the IP by 0.26 eV. The IPs for UO3 and UO2 are calculated to be 9.59 and 6.09 eV, respectively. The calculated IPs for MoO3 and WO3 are very similar, 11.13 and 11.11 eV, respectively, and MoO2 and WO2 are 8.51 and 8.79 eV, respectively. MoO2 has a triplet ground state, whereas WO2 has a singlet ground state. The calculated IP for NdO2 is 7.90 eV. NdO3 does not achieve a high +VI formal oxidation state on the lanthanide and has an IP of 7.80 eV. These calculated IPs are expected to have error bars of +/- 0.04 eV.