This paper presents experimental measurements of argon and oxygen gas flow through a 10 nm polycarbonate membrane, which are an order of magnitude higher than would be predicted by Knudsen diffusion alone, but may be described as ratified diffusion with slip (Knudsen-Smoluchoski diffusion). We also simulate the Poiseuille gas flow using a finite element based model and find that the hydrodynamic model may successfully predict Knudsen-like diffusion for Knudsen numbers as high as 10, contrary to conventional wisdom about the limitations of continuum models in the ratified regime. With the addition of slip boundary conditions, the model is able to describe the data with a similar tangential momentum accommodation coefficient (TMAC) as predicted by Knudsen-Smoluchoski diffusion. Transient measurements show that the pressure decay can be expressed by two distinct time constants, both of which indicate a faster decay than predicted by the Knudsen-Smoluchoski relations. The fact that the hydrodynamic model can successfully predict measured flow characteristics while conventional Knudsen-Smoluchoski ratified gas transport fails demonstrates that the hydrodynamic model may be extended into the nanoscale regime even at low gas density. (c) 2005 Elsevier B.V. All rights reserved.