No. 6 Residual Fuel Oils marketed in the United States contain an average sulfur content of about 1.6 percent, with a range encompassing a minimum of about 0.4 percent to a maximum of about 4.5 percent. The emission of sulfur dioxide from furnaces burning such fuel is recognized as a cause of significant air pollution. The objective of the study is to establish costs for reducing the sulfur content of fuel oils manufactured from high sulfur crudes. The desired maximum sulfur content for an acceptable fuel oil has been taken to be 0.5 wt. percent for this study. Presented are eight case studies developed in detail with the aid of a Linear Programming model of a typical 100,000 barrel per day modern refinery. (Author)