ABSTRACT In studying the flow of foam in unconsolidated porous media Khatib et al have shown that the destruction of foam lamellae depends on the gas/surfactant solution flowrates, fluid mobilities, and rock capillary pressure. This paper examines this flow regime, which we call the coalescence regime, in more detail. We have found that all published data referring to foam flow in consolidated media are consistent with a generalisation of Khatib's model. This new model is described in this paper. Two and three phase steady-state foam mobility models have been developed which exploit the dominant role of the foam coalescence mechanism. These models are based on published data for foam flow. The mobility models are then used in a finite difference, three phase, multi-component simulator. The simulator is applied to show that it can reproduce the generic transient foam behaviour observed in core floods. Calculations are then used to examine some of the important issues that have to be considered when designing field applications of foam flooding.