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Sulfated ash test method (ASTM D 874) has long been used as a quantitative measure of the ash forming metallic constituents in the lubricating oils and additives. This method provided predictable and chemically understood salts when additives which are based on the older additive technology (primarily Ba, Ca, Zn and P) are ashed. New additive technology has introduced other elements, such as Mg, B, etc., which resulted in the formation of non-stoichiometric oxides, phosphates, pyrophosphates, etc. in addition to the metal sulfates. X-ray diffraction analysis done on sulfated ash residues of these new additive packages clearly shows the presence of these non-stoichiometric mixed salts. This results in the experimentally obtained sulfated ash values being quite different (as much as 18% lower) than what would be predicted when the individual compounds are ashed separately.