The oxygen-ionic conductivity of perovskite-type La1-xSrxGa0.80-yMgyM0.2O3-delta (x = 0-0.20, y = 0.15-0.20, M = Fe, Co, Ni) and La0.50Pr0.50Ga0.65Mg0.15Ni0.2O3-delta in air, determined by the measurements of total conductivity, faradaic efficiency and oxygen permeability at 973-1223 K, increases with increasing concentration of the acceptor-type dopants, within the solid solution formation limits. The level of ionic conduction in these phases is, however, lower than that in parent compounds, La1-xSrxGa1-yMgyO3-delta, probably due to partial oxygen-vacancy ordering and a higher average cation-anion bond energy in transition metal-containing gallates. The activation energy for ionic transport in La1-xSrxGa0.80-gammaMgyM0.20O3-delta varies in the range of 126-171 kJ mol(-1). For compositions containing different transition metal cations, the ionic transport increases in the sequence M = Co < Fe < Ni, with the maximum ionic conductivity observed for La0.90Sr0.10Ga0.65Mg0.15Ni0.20O3-delta perovskite. (C) 2003 Elsevier B.V. All rights reserved.