Recently, with increasing worldwide consumption of oil and the ongoing aging of transport fleets, a number of oil spill accidents have had highly negative effects on ocean and coastal environments. In 1997, for example, anacc ident involving the Russian tanker Nakhodka occurred in very rough mid -winter sea conditions in the Sea of Japan just off the Japanese coast. The recovery operation was hampered by high waves, and the biggest problem was the lack of equipment capable of c ollecting spilled oil in stormy weather. In 1998 the Association for Structural Improvement of the Shipbuilding Industry (ASIS) initiated a research and development project on large -scale oil recovery systems for severe sea conditions, based on grants from the Japanese Ministry of Transport. One of the items included in this project is research and development for oil booms to be used in severe sea conditions. This report presents the results of associated work carried out in fiscal 1998, the goal of whi ch was to develop concepts of high performance oil boom and operation system. First, several kinds of basic measurements on oil containment performance using pellets were carried out in an experimental tank in order to evaluate the oil boom type, and oil containment performance data were also obtained. Next, basic experiments of oil boom system in rough sea using actual oil were performed in a tank to decide the appropriate concept among them. Finally, based on these experiments, basic design for the operation system was undertaken.