Introduction On March 24@ 1989 the Exxon Valdez ran aground Bligh Reef in Alaska's Prince William Sound@ spilling more than ten million gallons of crude oil. Congress' response to the Valdez spill was to Unanimously pass the Oil Pollution Act of 1990 (OPA). OPA contains many provisions that are aimed at directly or indirectly reducing oil spills. It raises liability limits and penalties for oil spills@ mandates changes in vessel manning and vessel equipment@ requires double hulls on all newly constructed tankers@ and phases-out single-hulled tankers. It also directs the Coast Guard to investigate whether structural changes would be an economically and technologically feasible way to reduce the size of oil spills from single-hulled vessels. To do this@ the Coast Guard awarded a contract to ICF Kaiser (ICF) and M. Rosenblatt and Son (MRS). The study@ referred to here as the ICF study@ calculated the cost-effectiveness of several structural modifications. The ICF study@ while very thorough@ had at least two significant weaknesses. First@ it did not properly estimate the amount of oil that would be spilled if no vessel modifications were undertaken. Second@ it did not put a@ dollar value on the benefits of reducing oil spills. The purpose of the paper is to address these issues and produce a complete cost-benefit analysis. This study proceeds by developing an economic framework for considering oil spill reduction. It then summarizes the primary federal law for preventing oil spills@ the Oil Pollution Act@ from an economic perspective. Next@ the paper analyzes the costs and benefits of structural modifications to single- hull tankers. This involves reviewing the regulatory analysis performed by ICF and then revising and extending the ICF analysis. The results are discussed in the last chapter.