Reactions of Me2+ cations with O-2 in molten (KBr + NaBr) (0.5:0.5) and (KBr + LiBr) (0.4:0.6) mixtures at T = 973 K were studied by potentiometric titration method using Pt(O-2)vertical bar ZrO2(Y2O3) indicator electrode. In the former melt, the set of cations available for investigation was wide enough (Me = Sr, Ca, Mn, Co, Ni and Pb) and the corresponding solubility product indices (pK(s,MeO), molalities) were found to be (3.81 +/- 0.3) (SrO), (5.00 +/- 0.3) (CaO), (7.85 +/- 0.3) (MnO), (8.80 +/- 0.1) (CoO), (9.72 +/- 0.04) (NiO) and (5.20 +/- 0.3) (PbO). A correlation between pKs, MeO and the polarisation action of the metal cation by Goldschmidt (Zer(Me2+)(-2)) was obtained. The oxide solubilities on the mole fraction scale were shown to be close to those obtained in molten (KCl + NaCl) equimolar mixture. On the basis of the solubility data the oxobasicity index (primary medium effect for oxide ion) for the (KBr + NaBr) melt was estimated as pI[KBr LiBr] = -0.24. Due to considerable oxoacidic properties of Li+ cation in the molten (KBr + LiBr) eutectic, it was possible to study only three from the above cations (Me = Mn, Co and Ni) and their pK(s,MeO) values were (4.36 +/- 0.2), (5.19 +/- 0.05) and (6.25 +/- 0.03), respectively. Comparison with the corresponding data for (KBr + NaBr) equimolar mixture showed that the Li+-based melt dissolved all the studied oxides in more extent. On the basis of the data obtained, the oxobasicity index value pI{KBr LiBr} was estimated as (3.01 +/- 0.5), that was close to the similar parameter of the chloride analogue (KCl + LiCl) (3.36). The change of the constituent anion of the melt in Cl -> Br does not result in appreciable changes of the melt acidity. Oxoacidic properties of the bromide melts rise in the following sequence: (2CsBr + KBr), pI(L) = -1.15 -> (KBr - NaBr), pI(L) = -0.24 -> (KBr - LiBr), pI(L) = +3.01. (C) 2014 Elsevier Ltd. All rights reserved.