The use of dynamic simulation as a risk modeling tool was a unique aspect of the Prince William Sound (PWS) risk assessment. The simulation technique enhanced the estimation of risk due to situational interactions (such as adverse weather, traffic) and allowed the systemwide impact of dynamic interventions such as closure restrictions and escort requirements to be measured. The PWS risk assessment project was a joint project of Det Norske Veritas, Rensselaer Polytechnic Institute, and the George Washington University. Seven accident types were considered in the PWS risk assessment: collision, powered grounding, drift grounding, foundering, structural failure, allision (i.e., a ship running into a stationary ship), and fire or explosion. The PWS risk assessment differentiates between triggering events (incidents) and events with direct adverse consequences (accidents). The study scope addressed the risks of marine oil transportation from the Valdez Marine Terminal to 20 mi (32.2 km) outside of Hinchinbrook Entrance. It examined causal and contributory factors such as marine traffic, weather, external environmental variables, human error, and mechanical failure. The study included technical and operational aspects of the tanker fleet, regulatory requirements, and operating company management. The project approach integrated a system-oriented simulation-based methodology with more traditional statistical and event-oriented probabilistic methods. Historical data analysis and structured expert judgment were used to support each element of the modeling process.