The formation of Oil Particle Aggregates (OPAs) is a natural process in which fine particles interact on available oil surfaces. 2 This process was described in the 1970s, but its full significance in the break-down of oil in the natural environment was not appreciated until 1990 during the Exxon Valdez response. 3 The OPA process has since been verified by dozens of laboratory studies 4 and a major multi-nation field experiment in Norway in 1997 5 . OPA formation is a significant weathering process because the result is a rapid increase in the surface area of the oil that is available for natural dispersion, biodegradation, and photo-oxidation.
