Two-dimensional surface waves were produced on a falling laminar water film by input of controlled disturbances, and the increase in the film absorption of the surrounding gas was determined at temperatures, 17.1-18.4 degrees C. The augmentation decreases constantly with wave frequency for low Reynolds numbers Re < 20, whereas it constantly increases for higher Reynolds numbers Re > 20. Taking account of these experimental results and the numerical observations by Nagasaki and Hijikata (1990, Proceedings of the 3rd Japan Mechanical Engineering Society Symposium on Numerical Dynamics, No. 900-69, pp. 47-48) and others, we constructed a double boundary layer model, in which the mass transfer coefficient k(L) is expressed as k(L) = xi root 3.46Df(w)/pi, where D and f(w) are the diffusivity in the film and the frequency of the waves, respectively. The equation, which is derived from the penetration theory, introduces the parameter xi for waves sweeping highly concentrated thin layers on the surface. It was found that at constant physical properties of liquid the parameter is a function only of phase velocity, and thus increases with phase velocity.