Quasi-elastic neutron scattering (QENS) has been used to study the diffusion of n-octane in silicalite. A larger diffusivity is found when compared with previous experiments performed in Na-ZSM-5, by a factor of 4. MD simulations have been performed for n-butane, n-hexane, and n-octane in silicalite and in a model zeolite with atomic defects to mimic the steric hindrance due to extra-framework cations in ZSM-5. The new QENS measurements and the MD simulations explain to a large extent the discrepancy previously observed for n-octane in MFI-type zeolites. (c) 2005 Elsevier B.V. All rights reserved.