Abstract: Improved methods of treating water and hydrocarbon producing subterranean formations to reduce the water permeability thereof are provided. The methods basically comprise introducing into the formation a water flow resisting chemical which attaches to adsorption sites on surfaces within the porosity of the formation and reduces the water permeability thereof without substantially reducing the hydrocarbon permeability thereof. The water flow resisting chemical is comprised of a polymer of at least one hydrophilic monomer and at least one hydrophobically modified hydrophilic monomer.