The tanker “Sea Empress” grounded at the entrance to Milford Haven in February 1996, releasing 72 000 t of Forties blend crude oil and 480 t of heavy fuel oil into the waters of southwest Wales. An estimated 15 000 t of emulsified oil came ashore along 200 km of coastline. A fishery exclusion zone was established to protect consumers of fish and shellfish, and monitoring was instigated in order to establish the degree and spread of contamination. A wide range of further studies were conducted with the aim of assessing the overall impact of the spill. In this paper we report on the establishment and subsequent lifting of fishing restrictions and the results of the fish and shellfish monitoring programme. The application of a range of biological effects techniques which illustrated sublethal impacts is also described. In retrospect, the impact of the spill was much less than would have been expected from the quantity of oil spilled. This was due to the circumstances of the spill, which led to fresh crude oil, amenable to chemical dispersion, being released during each ebb tide and carried into deep water to the south of Milford Haven. This enabled the extensive dispersant spraying operation, which included the aerial application of 446 tof chemical oil dispersant in order to enhance the rate of natural dispersion of the oil. This reduced the impact of the spill by preventing an additional 57 000 to 110 000 t of emulsified oil from impacting the beaches.