In this work we present a numerical study to investigate the motion of single Taylor bubbles in vertical tubes. A complete description of the bubble propagation in both stagnant and flowing liquids was obtained. The shape and velocity of the slug, the velocity distribution and the distribution of local wall shear stress were computed and compared favourably with the published experimental findings. The volume of fluid (VOF) method implemented in the commercial CID package, Fluent is used for this numerical study. (c) 2005 Elsevier Ltd. All rights reserved.