The mixed conductivity and oxygen permeation properties of Pr-deficient Pr1.9Ni0.71Cu0.24M0.05O4+delta (M = In, Ga, Al, Ni) were investigated. Among the dopants studied, the Ga-doped membrane was a superior mixed conductor, and it exhibited a high oxygen permeation rate compared with that of the other compositions. Examinations of membranes with different Ga concentrations revealed that the A-site cation-deficient composition, Pr1.9Ni0.71Cu0.24Ga0.05O4+delta, had the highest permeability of 286 mu mol min(-1) cm(-2) (ca. 7 cm(3) min(-1) cm(-2)) from air to He at 1273 K in a 0.5 mm thick membrane. The oxygen permeation rate of Pr1.9Ni0.71Cu0.24Ga0.05O4+delta decreased with thickness, indicating that the limiting factor is oxygen diffusivity in bulk. The Seebeck coefficient and oxygen permeation measurements suggest that the Ga dopant and Pr deficiency decreased the charge carrier density and improved the oxide ion conductivity. The estimated oxide ion conductivity in this material is a few times higher than that of the conventional mixed conductors such as Co-based perovskite. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3251004] All rights reserved.