Oxygen permeation measurements were performed on two layered bismuth based oxide ceramics: a rhombohedral phase belonging to the Bi2O3-CaO system. (Bi2O3)(0.73)-(CaO)(0.27) (BICAO) and a BICOVOX phase. Oxygen permeability for these systems was compared to permeability of the cubic fluorite type structure with composition (Bi2O3)(0.75)(Er2O3)(0).(25) (BE25). Low oxygen permeability was observed for the pure ceramic. As for BE25, permeability was considerably increased if 40 vol.% of silver was added to BICAO. In contrast, permeability was not improved by addition of gold to BICOVX. For this latter phase, the oxygen molecular exchange at the surface is clearly the limiting step in the oxygen transfer. (c) 2005 Elsevier B.V. All rights reserved.