Transport of gases through porous materials that exhibit bimodal pore size distribution is determined by a combination of molecular, Knudsen and/or micropore diffusion. To isolate the mechanism of mass transport through such materials, transport rates of small alkane hydrocarbons were measured through single pellets of industrial adsorbents SA and 13X in a Wicke-Kallenbach set up. Experiments were performed with dry pellets as well as pellets with different levels of water loading to block the micropores present in the material. Transient responses were shifted due to water loading. Steady-state apparent effective diffusivity in 13X pellet was also affected. Macropore-micropore-macropore and micropore in series model was used to explain experimental observation.