Molecular dynamics simulations have been performed to investigate oxygen transport in (UxPux−1)0.95Gd0.05O1.975, (UxThx−1)0.95Gd0.05O1.975 and (PuxThx−1)0.95Gd0.05O1.975 between 1000 and 3200 K. Oxygen diffusivity and corresponding activation energies are examined and compared to values for the undoped (UxPux−1)O2, (UxThx−1)O2 and (PuxThx−1)O2 systems where compositions between end members display enhanced diffusivity. Below the superionic transition oxygen diffusivity for the Gd doped systems is orders of magnitude greater compared to their undoped counterparts. However, enhanced diffusivity for doped mixed actinide cation compositions is not observed compared to doped end members. Changes in activation energy suggest changes in diffusion regime, which correspond to the creation of thermally activated oxygen defects.