TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThere is a great interest in the oil production industry in relative permeability modifiers (RPM) that can preferentially reduce water production without significantly affecting oil production. Various hydrophilic polymers have been studied for their RPM properties. This paper shows the potential of foam as RPM. Foams stable for a long time in presence of flowing water were developed using polymeric surfactants. Scale-up calculations show foam lifetimes long enough in field geometries for the process to be practicable. Foam tolerance to residual oil in water producing zones was produced by adding anionic surfactant to a nonionic polymeric surfactant. Resistance to flowing oil was, however, found to be unexpectedly high due to stable emulsion generation in porous medium. A process modification is shown to reduce the severity of this problem.