A family of Sr-doped perovskite compounds Ln 1−x Sr x CoO 3−δ (Ln=La 3+ , Pr 3+ and Nd 3+ ; x>0.60), were prepared by sol–gel chemistry and reaction at 1100°C under 1atm of oxygen. This structural family has been shown to be present only for rare earth ions larger than Sm 3+ and an upper limit of Sr 2+ solubility in these phases was found to exist between x=0.90 and 0.95. X-ray diffraction shows oxygen-deficient, simple cubic (Pm-3m) perovskite crystal structures. The combination of electron and powder neutron diffraction reveals that oxygen vacancy ordering occurs, leading to a tetragonal (P4/mmm) superstructure and a doubling of the basic perovskite unit along the crystallographic c-axis. No additional Ln 3+ /Sr 2+ cation ordering was observed.