The sinking of the supertanker Prestige off the coast of Spain in November 2002 was one of the most devastating oil spills ever worldwide. During any crisis most of the decisions have to be taken with limited information and they can benefit greatly from a rational methodology based on the available information. The main mechanisms involved in oil spill impacts are reviewed and we propose a decision tree based only on scientific criteria and data that are expected to be available in the first moments of an oil spill crisis. In the Prestige crisis, one of the decisions taken was to sail the Prestige out to sea. This paper makes an independent analysis of that decision to illustrate the methodology proposed, which may help decision making in future emergency situations.