- Statistical thermodynamics and density functional theory (DFT) formalisms are combined to analyze the phase competition of energetically preferable phases in (La1 − c,Src)CoO3 solid solutions upon LaCoO3 doping with Sr. La/Sr sublattice in ABO3 perovskite structure is considered as immersed in the field of CoO3 units and the superstructures that are stable with respect to the formation of antiphase domains are analyzed. The concentration-dependent energy parameters determining the relative stability of the cubic superstructures (phases) are extracted. This allows us calculations of concentration- and temperature dependences of the long-range order (LRO) parameters for different phases. The temperatures of the order–disorder phase transformations for energetically stable at T = 0 K phases are obtained. It is shown that the phase corresponding to the (La0.875,Sr0.125)CoO3 composition may exist at low temperatures. Nevertheless, already at room temperature it fails in the phase competition with the disordered (La1 − c,Src)CoO3 solid solution and the phase corresponding to the (La0.75,Sr0.25)CoO3 composition and thus hardly can be observed.