ABSTRACT The most important objectives of the International Maritime Organization (IMO) have been improving maritime safety and preventing marine pollution. The Marine Environment Protection Committee (MEPC), which is responsible for coordinating IMO's activities in preventing and controlling marine pollution from ships, agreed that spills of 100 tons of oil or more should be regarded as “significant.”1 Analyses of significant oil spills (more than 100 metric tons) from ships have helped develop spill statistics, categories of spill incidents, geographical data on spills, and so on. Analyses for the past 10 years show that about 75 percent of the incidents were caused by grounding, collision, and breakdown; about 8 percent were caused by operational errors while loading, discharging, or washing tanks; and about 17 percent were due to rough weather, fire, and other causes. These analyses suggest that measures can be taken to prevent oil pollution from ships chiefly by improving safety standards for ship construction, equipment, and operation. This paper analyzes several incidents to understand the causes, actions taken, and results of oil spills in different circumstances and with different types of oil. It also examines IMO's achievements in combating oil pollution and the difficulties that have been met in implementing Annex I of the Regulations for the Prevention of Pollution by Oil, the International Convention for the Prevention of Pollution from Ships, 1973, as modified by the Protocol of 1978 (MARPOL 73/78).