For a reliable description of mass transfer in membrane reactors the multilayer structure of the membrane is essential. This paper discusses methods which are sufficient to distinguish between homogeneous and composite membranes, and some others which are not. Different mass transport experiments (single gas permeation, isobaric diffusion, transient diffusion) with a porous metallic membrane consisting of two layers and the dusty gas model were used for this purpose. Simultaneous identification of mass transport parameters of both layers was achieved by modern optimization techniques on single gas permeation data. These parameters were validated by isobaric or transient diffusion measurements.