Stratified two-phase gas-liquid flow in three-dimensional (3D) is challenging because of the difficulty in determining the shear stresses at the walls and at the gas-liquid interface. The study is simplified by considering only the gas and the gas-liquid interface. The gas flows between the fixed wall of the pipe and the interface, which is regarded as wall moving at liquid velocity. It is shown, using a CFD code, that one can determine the correct horizontal and vertical profiles of the longitudinal velocity of the gas. Seven experiments done by Strand (1993) for a horizontal stratified gas-liquid flow are simulated. The simulation results are compared with experimental results, and also to the numerical results of Meknassi et al. (2000). We deduce from these comparisons that the approach suggested in this work is very valuable. Then expressions for calculating the gas-wall friction factor, and the gas-liquid interface friction factor are presented. These factors are crucial for evaluating the shear stresses. It appears, after comparison with the experimental values that the correlation proposed for calculating the friction factor at the interface, in the present work, agree with the experimental values better than that given by Taitel and Duckler (1976a, b). (C) 2010 Elsevier Ltd. All rights reserved.