This method is for determining disulfide sulfur in gasoline, liquefied petroleum gas (LPG), and other light petroleum distillates. Part A of the method, an acid stirring procedure, is used for low molecular weight disulfides usually found in LPG and for distillates that do not contain tertiary disulfides. Because of its rapidity, the acid stirring procedure is recommended for routine work where tertiary disulfides are not a factor. Part B of the method, an acid reflux procedure, is reserved for samples containing tertiary disulfides. This method is applicable to samples containing a disulfide sulfur concentration of 10 mass-ppm or greater.