"This report, which is the first concerning the work of American Petroleum Institute Research Project 48A on the separation and identification of sulfur compounds in crude iol, is in the nature of a survey to determine the types of sulfur compounds that may be expected to be found in naphthas from high-sulfur crude oils. The distribution of free sulfur, hydrogen sulfide, mercaptans (thiols), disulfides, two types of sulfides having different activities, and residual (less reactive) sulfur compounds has been determined for naphthas, 482 degrees F. (250 degrees C.) end point, from 17 typical high-sulfur crude oils of the United States and Middle East. The naphthas included straight-run distillates produced in the laboratory from a number of crude oils by distillation both at atmospheric pressure and at very low pressures (0.5 to 2.0 mm of mercury), so that comparative data were obtained showing the effect of heating to the temperatures attained in the ordinary distillation of naphtha. The results indicate a wide range in the proportion of the different types of sulfur compounds. However, many of the oils or naphthas contain predominantly sulfides and mercaptans, while relatively few contain appreciable quantities of disulfides. Two are characterized by large quantities of free sulfur. Although many changes in the sulfur compounds present may occur during distillation, the most obvious and interesting one is the almost universal decrease in the content of that unreactive sulfur group called “residual sulfur,” in the naphthas produced at atmospheric pressure as compared to those obtained at reduced pressure. In general, this reduction in residual sulfur shows up as sulfide sulfur in the distillate made at atmospheric pressure."