In this paper we report the successful synthesis of the cubic oxyanion containing perovskites, Ba₂Sc_2−xP_xO₅₊x (x = 0.4, 0.5), with the samples analysed through a combination of X-ray diffraction, NMR, TGA, Raman spectroscopy and conductivity measurements. Conductivity measurements indicate a p-type contribution to the conductivity in oxidizing conditions at elevated temperatures, with evidence for proton conduction in wet atmospheres. For the latter, bulk conductivities of 5.9 × 10⁻³ and 1.3 × 10⁻³ S cm⁻¹ at 500 °C were obtained for x = 0.4 and 0.5 respectively, comparable to other perovskite proton conductors, while the stability towards CO₂ containing atmospheres was improved compared to BaCeO₃ based systems. Related Si doped systems have also been prepared, although in this case small Ba₂SiO₄ impurities are observed. We also provide evidence to suggest that “undoped” Ba₂Sc₂O₅ contains carbonate groups, which accounts for its thermal instability.