A composition comprising expandable cross linked polymeric microparticles having an unexpanded volume average particle size diameter of from about 0.05 to about 10 microns and a cross linking agent content of about 6,000 to less than about 9,000 ppm of labile cross linkers and from 0 to about 300 ppm of non-labile cross linkers, useful for modifying the permeability of subterranean formations and increasing the mobilization and/or recovery rate of hydrocarbon fluids present in the formations.