The number of milligrammes of potassium hydroxide (KOH) that combine with one gramme of oil under conditions specified by test method ASTM D 94. Saponification number is an indication of the amount of fatty saponifiable material in compounded oil. Caution must be used in interpreting test results if certain substances - such as sulphur compounds or halogens - are present in the oil, since these also react with KOH, thereby increasing the apparent Saponification number.