Computer-modeling techniques have been used to investigate the defect and transport properties of the LaGaO3-based oxygen ion conductor. We consider a range of cation dopant substitutions with oxygen vacancy compensation. Favorable acceptor dopants ton energetic grounds) are predicted to be Sr at La and Mg at Ga, in accord with experimental work. The formation of dopant-vacancy clusters is examined with the lowest binding energy found for the Sr-vacancy configuration. Oxygen-vacancy migration is along the GaO6 octahedron edge with a curved trajectory sind a calculated mi,oration energy of 0.73 eV. We have also examined cation-vacancy transport, which reveals high migration energies (>4 eV). Hole formation from an oxidation process is calculated to be relatively unfavorable, which is compatible with experimental findings that show predominantly ionic conduction in doped LaGaO3. Furthermore, consideration of water incorporation suggests that proton conduction will not be significant in this material.