Conclusions. -In summary, measurable p-type conductivity is predicted to be achievable in BaSnO 3 , but due to the inevitable presence of oxygen vacancy defects it is unlikely to reach metallic-like levels, with hole densities capped at just under 10 16 cm -3 . Of the group 1 metals Li, Na and K, only the latter is predicted to be a reasonably good p-type dopant, with the former two undergoing self-compensation by low energy, n-type interstitial species.