Acceptor-type doping of perovskite-type La1-x,SrxGa0.80-y,MgyM0.20O3-delta (x = 0-0.20, y = 0.15-0.20, M = Fe, Co, Ni) leads to significant enhancement of the oxygen permeability due to increasing oxygen vacancy concentration and, thus, ionic conductivity. The increase in strontium and magnesium content is accompanied, however, with increasing role of the surface exchange kinetics as a permeation-limiting factor. At temperatures below 1223 K, the oxygen permeation (OP) fluxes through dense La(Sr)Ga(Mg,M)O3-delta membranes with the thickness less than 1.5 mm are mainly limited by the exchange rate at membrane/gas boundaries. For transition metal-containing La(Sr)Ga(Mg)O3-delta (LSGM) ceramics, the oxygen transport increases in the sequence Co < Fe < Ni. The highest permeation is observed for La0.90Sr0.10Ga0.65Mg0.15Ni0.20O3-delta perovskite membranes, which exhibit level of the oxygen permeability similar to that of La(Sr)Fe(Co)O3-delta and La2NiO4-based solid solutions. The average thermal expansion coefficients (TECs) of La(Sr)Ga(Mg,M)O3-delta ceramics in air are in range (11.6-18.4) x 10(-6) K-1 at 373-1273 K. (C) 2003 Elsevier B.V. All rights reserved.