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Overall, oil spillage from vessels throughout the US has decreased significantly since 1990 and the enactment of the Oil Pollution Act of 1990 (OPA 90). Nearly 20 times more oil was being spilled annually by vessels in before 1990 than is currently being spilled. The number of spills of 500 gallons or more have decreased since 1990. The reporting of smaller spills has increased since 1985, but the incidence of these spills has decreased since 1990. The reasons for spill reductions with OPA 90 are varied and complex. There are reductions noted even before some of the prevention measures associated with OPA 90 have been implemented. There is speculation that these spill reductions may be related to the increasing costs of oil spills and unlimited liability, and the resulting greater “care ” that vessel owners and operators are exercising, as well as the higher class of vessels transiting US waters based on financial and insurance requirements. The vast majority of vessel spills are very small. Nearly 65 percent of spills are less than 10 gallons, 90 percent are less than 100 gallons. Smaller spills (under 100 gallons) make up only 0.7 percent of the total volume spilled. The very rare larger spills of one million gallons or more (less than one tenth of one percent in frequency) make up over 42 percent of the total volume spilled