A potentiometric titration method was used to determine the solubility products (pP = - log P) of some oxides at 700 degreesC in molten chloride mixtures of the following compositions, CaCl2-KCl (0.235:0.765); SrCl2-KCl-NaCl (0.22:0.42:0.36); BaCl2-KCl-NaCl (0.43:0.29:0.28); and BaCl2-KCl (0.26:0.74). On the basis of the solubility data, oxobasicity indices of the above melts were estimated as 4.05, 1.95, 2.01 and 1.83, respectively. The CaCl2-based melt possesses the upper limit of oxobasicity at pO similar to 1.3 caused by the precipitation of CaO. The features of calibration plots E-pO in the studied melts are discussed.