in Wiley InterScience (www.interscience.wiley.com).The article is devoted to a theoretical analysis of counter-current gas-liquid wavy film flow between vertical plates. We consider two-dimensional nonlinear waves on the interface over a wide variation of parameters. The main interest is to analyse the wave structure at the parameter values corresponding to the onset of flooding observed in experiments. We use the Navier-Stokes equations in their full statement to describe the liquid phase hydrodynamics. For the gas phase equations, we use two models: (1) the Navier-Stokes system and (2) the simplified Benjamin-Miles approach where the liquid phase is a small disturbance for the laminar or turbulent gas flow. With the superficial gas velocity increasing and starting from some value of the velocity, the waves demonstrate a rapid decreasing of both the minimal film thickness and the phase wave velocity. We obtain a region of the gas velocity where we have two solutions at one set of the problem parameters and where the flooding takes place. Both the phase wave velocity and the minimal film thickness are positive numbers at such values of the velocity. We calculate the flooding point dependences on the liquid Reynolds number for two different liquids. The wave regime corresponding to the flooding point demonstrates negative u-velocities in the neighbourhood of the interface near the film thickness maximum. At smaller values of the superficial gas velocity, the negative uvelocities take place in the neighbourhood of the film thickness minimumHere, Re ¼ 20 and k neut /L ¼ 0.25; (a) and (e) correspond to U GS ¼ 2.5 m/s; (b) and (f), U GS ¼ 7.0 m/s; (c) and (g) U GS ¼ 8.5 m/s; (d) and (h) U GS ¼ 9.07 m/s. Lines 1-3 correspond to water at k neut /L ¼ 0.25, 0.2, 0.15, respectively. Lines 4-6 correspond to 2.5% butanol at k neut /L ¼ 0.25, 0.2, 0.15, respectively.