Western Research Institute (WRI) has conducted exploratory experiments on the use of microwave-induced plasmas to desulfurize heavy oils. Batch mode experiments were conducted in a quartz reactor system using various reactive and nonreactive plasmas. In these experiments a high-sulfur asphalt was exposed to various plasmas, and the degree of conversion to distillate, gas, and solids was recorded. Products from selected experiments were analyzed to determine if the plasma exposure had resulted in a significant reduction in sulfur content. Exploratory experiments were conducted using reactive plasmas generated from hydrogen and methane and nonreactive plasmas generated from nitrogen. The effects of varying exposure duration, sample temperature, and location of the sample with respect to the plasma discharge were investigated. For comparative purposes two experiments were conducted in which the sample was heated under nitrogen with no plasma exposure. Distillates containing approximately 28% less sulfur than the feedstock represented the maximum desulfurization attained in the plasma experiments. It does not appear that plasma reactions using the simple configurations employed in this study represent a viable method for the desulfurization of heavy oils.