Foamed-gas injection is a promising technique for achieving mobility control and diverting fluid to low permeability strata within heterogeneous porous media. However, the factors most important for diversion have not been stated and explored definitively. Gas mobility in the presence of foam depends critically on foam-bubble size; bubble size may vary with permeability, porosity, surfactant type and concentration, and the velocity of liquid and gas. This paper adopts a local equilibrium, scaling perspective to describe quantitatively foamed-gas mobility within heterogeneous porous media. Conventional and percolation network scaling ideas are employed. A new closed form expression for the fraction of mobile gas within a foam is derived using statistical network concepts. Additional equations indicate, for instance, that porosity plays an important role in setting gas mobility because it reflects the relative abundance of foam germination and termination sites per unit volume of porous media. Liquid velocity is also important because gas mobility is inversely proportional to this factor.