In March 1989, North America's largest marine oil spill occurred in one of its largest estuaries: Alaska's Prince William Sound. Observations of the spill trajectory serve to delineate the circulation within the sound and along the southern coast of Alaska. This region has very high rates of freshwater discharge and intense wind stresses: the average annual amount of fresh water entering the Northeast Pacific drainage system is at least 20% larger than the Mississippi River system, and the seasonal signals of wind stress and wind stress curl here are the largest in the North Pacific. Even as the oil was being released in the sound, it came under the influence of this coastal circulation. The spilled oil and subsequently released surface drifters have served as tracers that can be used to examine our knowledge of the processes affecting regional coastal flow. This knowledge might be applied to coastal processes elsewhere.