In this paper, we discuss the effects of the defect interactions on the thermodynamic properties and electronic transport of nonstoichiometric oxides. We first show that two limited thermodynamic behaviours can be distinguished depending on whether the oxide has a metallic type electronic conduction or a hopping electronic conduction. In the first case, the interactions are expected to be short ranged because of the screening of the conduction electrons, while they are Coulombic in the second case. This paper is limited to this last case, exemplified mainly by M1−xO(M=Co, Mn,…) cubic oxides.