Lumps of crude oil residue floating the sea surface have been observed widely. Samples were taken with surface-skimming nets in the Mediter-ranean Sea and eastern North Atlantic Ocean; their displacement volumes were as large as 0.5 milliliter per square meter. An isopod, Idotea metallica, appears to be associated with the lumps, and a barnacle, Lepas pectinata, grows upon them. Lumps were found in stomachs of Scomberesox saurus, a surface-feeding fish importanit in ocean food webs. Films on the lumps, presumably consisting mostly of bacteria, consumed oxygen at the rate of 4 cubic millimeters per hour per square centimeter of lump surface. Chemical analysis suggested that certain lumps had been at large for only a few weeks; data from barnacle size and growth rate suggested that other lumps were at least 2 months old.