We model the occurrence of an environmental accident as a stochastic event, in particular the situation of an oil spill is explored. Characteristics of the ship operator, and the different types of the ship’s operating environment determine a stochastic process governing the time patterns and size of spills. It is shown that both the time distribution of different types of oil spills, and the distribution of spill size are affected by pollution control instruments such as fines, by enforcement effort, and by the alert level of the operating personnel.