In undoped, nominally stoichiometric, Li 3 OCl we predict that the dominant defect species varies with synthesis conditions; under Li-poor conditions the dominant negative defect species is V Li and the dominant positive defect species is V Cl ; under Li-rich conditions the dominant defect species are O Cl and V Cl . Under all considered synthesis conditions, we predict lithium vacancies to be present in much greater concentrations than lithium interstitials, in qualitative agreement with previous studies , and confirming V Li as the dominant charge carrier in nominally stoichiometric samples.