Defect energetics of Ba2In2O5 have been investigated by atomistic modelling techniques with emphasis on different modes of conductivity. Oxygen Frenkel pairs were found to be the most energetically favourable intrinsic defects and are responsible for oxide ion conductivity in the orthorhombic structure. Formation energies of electronic species suggest that Ba2In2O5 will oxidize readily to produce positive holes. Energies of proton incorporation reveal that Ba2In2O5 should also exhibit reasonable proton conductivity in moist atmospheres.