Turbulent gas-liquid stratified flow in near horizontal, straight ducts with a regular two dimensional wavy deformation of the interface has been studied. In this flow regime strong mean secondary currents are observed. By applying the Generalized Lagrangian Mean Theory of Andrews and McIntyre (1978a) it is shown that these secondary velocities in the liquid phase may result from an interaction between wave psuedomomentum per unit mass and mean axial velocity. This interaction takes exactly the same form as the Craik and Leibovich ’vortex forces’ (Leibovich 1983) for Langmuir circulation in the oceans, but with wave pseudomomentum per unit mass replacing Stokes drift. For a particular case it is shown that the wave pseudomomentum-mean flow interaction is identical to a wave Reynolds stress formulation. Predictions with a numerical implementation of the developed model compares favourably with the experimental results of Suzanne (1985).