There are three distinct classes of perovskite structured metal oxides, defined by the charge states of the cations: AIBVO3,AIIBIVO3, and AIIIBIIIO3. We investigated the stability of cubic quaternary solid solutions ABO3−A′B′O3 using a model of point-charge lattices. The mixing enthalpies were calculated and compared for the three possible types of combinations of the compounds, both for the random alloys and the ground-state-ordered configurations. The mixing enthalpy of the (I,V)O3-(III,III)O3 alloy is always larger than the other alloys. We found that, different from homovalent alloys, for these heterovalent alloys a lattice constant mismatch between the constituent compounds could contribute to stabilize the alloy. At low temperatures, the alloys present a tendency to spontaneous ordering, forming superlattices consisting of alternated layers of ABO3 and A′B′O3 along the [110] direction.