In continuation of our previous work on phase diagram investigations of alkali metal–alkaline earth metal–uranium oxides, the sub-solidus phase relations in K–Sr–U–O quaternary system were determined at 850^oC in air. A pseudo–ternary phase diagram of UO₃–SrO–K₂O was drawn using reported ternary compounds in K₂O–UO₃ and SrO–UO₃ systems, a single quaternary compound, K₈Sr₂U₆O₂₄ and various phase mixtures. These compounds and mixtures were synthesized by solid route, by heating K₂CO₃, SrCO₃ and UO₃ in different molar proportions at 850^oC. The phase fields of K₂O–SrO–UO₃ pseudo-ternary phase diagram were established by X-ray powder diffraction analysis. Gibbs energies of formation of binary and ternary uranates were estimated. The Gibbs energies of formations of A₈Sr₂U₆O₂4 (A = Na/K/Rb/Cs) type compounds for different alkali metals were compared to find a reason for the stability of the compound for sodium, potassium and rubidium and its instability for cesium.