The effect of evaporation on stratification in large liquid hydrogen storage tanks of different aspect ratios is computed. A homogeneous two-phase model is used and the continuity, momentum and energy equations for the two phases are solved. Evaporation at the liquid-vapor interface is incorporated through a source term for mass transfer. The amount of stratification is seen to progressively increase as the aspect ratio of the tanks increases. However, the surface evaporation brings down the differences in the amount of stratification with changes of aspect ratio. The predictions for stratification in the pre-evaporation and evaporation phases are discussed. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.