Many marginal gas wells cannot sustain production without artificial lift. For deep gas wells, one of the most feasible techniques is to use foam lift — inject surfactant in the well and create stable foam to lift the liquid to the surface. Unfortunately, no correlation is available to calculate the pressure drop under foam flow conditions. Conventional pressure drop prediction models are unable to correctly predict the pressure drop under these conditions. In this paper, a new model is developed to predict the pressure drop under foam flow conditions. By using a simple drift flux model and using some of the available literature data on foam, a foam pressure drop model was developed, and compared with 570 data points collected from many gas wells. The match between the model and the actual observations is reasonable. The model can be further improved if additional data on the foam quality, stability and the ability to entrain liquids becomes available.