The membrane thickness is one of the major parameters affecting hydrogen diffusion during electrochemical permeation tests. In this work, we study the effects of membrane thickness by comparing experimental results from the literature with a numerical analysis by finite element method (FEM). We consider the effects of a palladium coating or an oxide layer on the diffusion through a-iron, and we also studied the effects of an oxide layer on the diffusion through martensitic steels. Our model allows us to match the experimental data and determine the initial subsurface hydrogen concentration, trap densities, and the diffusivity of the layer. However, we had to consider the effects of the mechanical polishing on hydrogen trap densities and concentrations to ensure a reasonable correlation. The balance between the effects of trapping and the oxide layer are finally discussed; while hydrogen trapping increases the effective subsurface concentration, the oxide layer decreases its value. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.