Following the Exxon Valdez oil spill of March 24, 1989, in Prince William Sound, Alaska, Exxon conducted comprehensive, systematic shoreline surveys in cooperation with federal and state authorities to obtain information on the distribution and magnitude of shoreline oiling and to identify natural and cultural resources requiring special protection. Similar joint surveys were performed during the springs of 1990, 1991, and 1992 on all Prince William Sound and Gulf of Alaska shorelines that were suspected of having remnants of weathered oil and that would benefit from further cleanup. The extent of oiling declined substantially between 1989 and 1992: in 1989, survey teams found oil on about 16% (783 km) of the approximately 5 000 km of shoreline in Prince William Sound; in the spring of 1991, they found oil on about 96 km; and, in May 1992, on only about 10 km of shoreline in the sound. During this period, most of the oil was located in the biologically least productive upper intertidal and supratidal zones. In the springs of 1990, 1991, and 1992, isolated pockets of subsurface oil were found, chiefly in small scattered zones in coarse cobble/boulder sediments in the upper intertidal or supratidal zones. In 1991, about one-third of the subdivisions in Prince William Sound with surface oil also contained some subsurface oil. The areal extent of this subsurface oil declined by nearly 70% between 1991 and 1992, from about 37 000m2 to about 12 000m2. Moreover, where subsurface oil remained in 1992, it was present in lesser amounts. Rates of oil removal were greatest on coastal sections treated early in the spring and summer of 1989. Where shoreline treatment was delayed, the subsequent rate of removal of oil from the shore by natural processes was slower.