Gas displacement in the presence of surfactant under foaming conditions has been shown to enhance oil recovery. But it is a complex process because surface phenomenon is involved in it. The lack of understanding is a barrier for its commercial-scale testing and application. A major difficulty in analyzing the production performance of such displacement is in deciding whether to treat gas and surfactant solution as a two phase mixture or as a single phase homogeneous fluid (foam). Another uncertainty is in determining the rheological behavior of gas and surfactant solution mixture flowing in the porous media. The problem is further complicated if two-dimensional flow is taking place, since the frontal geometry may also influence the performance significantly. This study was performed to investigate these problems. Flow was visually observed through a two-dimensional (x,z) sandpack of four feet length and one foot height, having 14 darcies permeability and 35% porosity. Since analytical treatment of the flow and oil recovery data has not been possible, the objectives were to get a basic understanding of the flow behavior under foaming conditions, devise conceptual models with the help of flow processes seen, and then analyze the data quantitatively using semi-analytical approaches. A model meeting these objectives was developed and successfully matched with experimental data obtained in the two-dimensional sandpack. 125 refs., 36 figs., 21 tabs.