"INTRODUCTION The Petroleum Industry@ realizing the gravity of the air pollution problem@ is endeavoring to obtain factual information to aid both government and industry. Part of this effort is aimed at clarifying the confusion that exists today regarding cost data for desulfurization of residual fuel oils being burned along the East Coast. Following clarification@ it will be possible for government and industry to view the matter in the proper perspective and to formulate a sound course of action for the future. In view of the critical nature of the air pollution problem on the East Coast@ the American Petroleum Institute has sponsored this study to establish approximate costs and processing schemes for reducing the sulfur content of Caribbean residual fuel produced from Venezuelan crude oils. Bechtel Corporation has been selected to perform this study because of its knowledge and experience in this field@ and because it has computer programs readily available for performance of petroleum studies. Under contract to the Public Health Service@ Bechtel Corporation previously investigated the costs of reducing the sulfur content of residual fuel oils. A report covering these earlier results entitled ""The Economics of Residual Fuel Oil Desulfurization"" was published during June@ 1964. In this earlier work@ the emphasis was placed on studying domestic (U.S.) refining situations. Caribbean residual fuel oils typically have higher sulfur content and much higher metals content than residual fuels produced from domestic crude oils@ thus making desulfurization more difficult. It is envisioned in this current cost study that residual fuel oil desulfurization facilities will be located in the various Caribbean refineries currently shipping these oils to the United States. This appears to be a logical choice@ because blending components may then be interchanged between the various refined products to allow optimum blending. As Federal regulations prohibit processing residual fuel oil after importation into the United States@ such an alternative was not considered in this study. The general approach in developing this study was to: 1. Define a typical Caribbean refining situation (Base Case Refinery)@ in terms of location@ size@ process units@ product yield structure@ crude oil charge@ and product specifications. 2. Impose on this typical Base Case Refinery various sulfur specifications for the residual fuel oil@ keeping other specifications and all product demands constant. 3. Develop various processing schemes and desulfurization costs@ with the calculations based on the required incremental additions to the Base Case Refinery@ as defined in this study Because of the vital interest in this problem by the U.S. Public Health Service@ they were asked to give their guidance and to review the study plan and subsequent results"