The present investigation was undertaken because the customary determination of thiophenic sulfur by extraction with mercuric nitrate cannot be used on shale oil naptha as the large quantities of olefins present react with the reagent. In an ordinary group sulfur analysis of shale oil naphtha, therefore, the thiophenic sulfur is classed with the residual group that is not determined directly. As most of the sulfur in shale oil naphtha falls in this group, a direct determination of thiophenic sulfur is desirable.