Gas dissociation with a ceramic membrane is an economical and environmental attractive process for methane gas conversion into syngas (mixture of H-2 and CO). For this application, the membrane materials require mixed ionic and electronic conductivities in a large range of pO(2) resulting in an excellent oxygen semi-permeation of the membrane to improve methane conversion. In this paper, particular attention is given to the influence of sealant materials on oxygen semi-permeation performances of membrane materials. For instance, oxygen semi-permeation measurements have been performed with La0.8Sr0.2Fe0.7Ga0.3O3-delta membranes under an oxygen partial pressure gradient at temperatures from 700 C to 1000 degrees C with different sealing materials (glass or gold ring sealant) between the membrane and the support. The result leads to a better understanding of the effects of sealing on oxygen transport through the La0.8Sr0.2Fe0.7Ga0.3O3-delta membrane. Indeed, a gold sealing material is required for accurate measurements of oxygen semi-permeation flux. (C) 2010 Elsevier B.V. All rights reserved.