This study compares the individual desorption kinetics in terms of effective diffusional time constants (D-eff/r(2)) of 20 linear and multi-branched alkanes through a carbon molecular sieve (CMS) material obtained by the zero length column (ZLC) technique. As is typical for microporous materials with pore sizes under 0.6 nm, the effective diffusivity decreased as the carbon number increased in each hydrocarbon family. However, comparing hydrocarbons with the same carbon number, the effective diffusivity tended to increase as the number of branches increased. In this case, the physisorption of the different alkanes on the carbon molecular sieve may be the result of multiple pore mouth adsorption modes. Each mode depends on the number of carbon atoms inside and outside the pore mouth cavity and the interactions between these branched hydrocarbons and the carbon walls. (C) 2012 Elsevier B.V. All rights reserved.