Abstract: This invention is directed to a composition comprising expandable polymeric microparticles comprising an interpenetrating polymer network (IPN). The IPN constrains the microparticle to an unexpanded volume average particle size diameter of from about 0.05 to about 5,000 microns. Labile cross-links in the polymers of the IPN are subject to degradation, which results in release of the expandable microparticle so that the microparticle expands. The invention is further directed to the use of the composition for modifying the permeability of subterranean formations and increasing the mobilization and/or recovery rate of hydrocarbon fluids present in the formations.