The report addresses the methods that can be used for making such estimates of input and the difficulties and uncertainties involved. Ship-based activities are the primary focus. These activities include ships, offshore oil and gas exploration and production, and the onshore facilities related to both operations, including refineries and all associated infrastructures. Estimation of operational ship inputs, both cargo and ship related, was a primary focal point of this study and required knowledge of vessel types and structures, operations, the oil trade, and MARPOL 73/78 regulations. Data on other inputs were obtained from many sources, published and unpublished. Considerable effort has been made to assemble data and conduct trend analysis of accidental spills from ships and other sea-based activities, from the late 1960s onwards.