Show Menu Show Menu Close Menu Close Menu Facebook Facebook Twitter Twitter LinkedIn LinkedIn Search Search Contact Contact
Savant Labs
A World of Lubrication Understanding®

ASTM D94 - Saponification Number of Petroleum Products

Significance and Use

5.1 Petroleum products can contain additives that react with alkali to form metal soaps. Fats are examples of such additives. Also, certain used engine oils, especially from turbine or internal combustion engines, can contain chemicals that will similarly react with alkali. The saponification number ex-presses the amount of base that will react with 1 g of sample when heated in a specific manner. This then gives an estimation of the amount of acid present in the sample, that is, any free acid originally present plus any combined (for example, in esters) that have been converted to metal soaps during the heating procedure.

 5.2 Saponification numbers are also used in setting product specifications for lubricants and additives.


 1.1 These test methods cover the determination of the amount of constituents in petroleum products such as lubricants, additives, and transmission fluids that will saponify under the conditions of the test.

 NOTE 1—Statements defining this test and its significance when applied to electrical insulating oils of mineral origin will be found in Guide D117. Experience has shown that for transformer oils, Test Method D94, modified by use of 0.1 M KOH solution and 0.1 M HCl, is more suitable.

 1.1.1 Two test methods are described: Method A—Color Indicator Titration (Sections 6–13), and Method B—Potentiometric Titration (Sections 14–23).

 1.2 Because compounds of sulfur, phosphorus, the halogens, and certain other elements that are sometimes added to petroleum products also consume alkali and acids, the results obtained indicate the effect of these extraneous materials in addition to the saponifiable material present. Results on products containing such materials, on used internal-combustion-engine crankcase oils, and on used turbine oils must be interpreted with caution.

 NOTE 2—The materials referred to above, which are not normally considered saponifiable matter, include inorganic or certain organic acids, most non-alkali soaps, and so forth. The presence of such materials increases the saponification number above that of fatty saponifiable materials for which the test method is primarily intended. The odor of hydrogen sulfide near the end of the back-titration in the saponification test is an indication that certain types of reactive sulfur compounds are present in the sample. In the case of other reactive sulfur, chlorine, and phosphorus compounds and other interfering materials, no simple indication is given during the test. A gravimetric determination of the actual amount of fatty acids is probably the most reliable method for such compounds. Test Methods D128 or IP Method 284/86 can be used to determine fatty acids gravimetrically.

1.3 The values stated in SI units are to be regarded as the standard.

Extracted, with permission, from ASTM D94-07 - Saponification Number of Petroleum Products, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be purchased from ASTM International,