Results are presented of computer simulation studies of some uranium oxide phases, using two contrasting methods to calculate defect parameters. The first is based on the Mott-Littleton approach, which assumes defects to be in infinite dilution in an otherwise perfect lattice, and the second allows finite defect concentrations to be modelled, using a supercell approach. Two groups of uranium oxide compounds are studied; firstly the mixed oxide reactor fuel (U,Pu)O2, where lattice and defect properties are obtained as a function of Pu concentration, and secondly the alkaline earth metal uranates M3UO6, where the calculation of a complete set of structural data and defect parameters is described, and the dominant mode of intrinsic disorder proposed.