This invention is directed to a composition comprising expandable polymeric microparticles comprising hydrophobic polymers having a backbone with labile pendant groups, the microparticles having an unexpanded volume average particle size diameter of from about 0.05 to about 5,000 microns. Labile pendant groups on the backbone are subject to hydrolysis under a change in environmental conditions that results in expansion of the microparticle. 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.