Studies of oxide solubilities (methods and results) in molten alkaline chlorides are considered. The scatter of literature data on oxide solubilities in molten KCl-NaCl has been explained by the effect of crystal grain sizes on their solubilities according to the Ostvald-Freindlich rule. Author’s results of systematic oxide solubilities’ studies in molten alkaline halides (KCl-NaCl, CsCl-KCl-NaCl, CsBr-KBr, CsI) are considered. Oxide solubilities in molten alkaline halides (pP) have been found to vary linearly with corresponding cation radii; such plots might be proposed for estimations of oxide solubilities in molten alkaline halides.