This International Standard specifies a method for the determination of the ash content of petroleum products, such as distillate and residual fuel oils, crude petroleum, lubricating oils, waxes and other petroleum products, in which any ash-forming constituents present are normally considered to be undesirable impurities or contaminants. Ash can result from oil-soluble or water-soluble metallic compounds or from extraneous solids such as dirt and rust. The method is applicable to products having ash contents in the range 0,001 % (m/m) to 0,180 % (m/m), but does not apply to products which contain ash-forming additives, including certain phosphorus compounds. The analysis of unused or used lubricating oils containing additives, used engine crankcase oils, lubricating oils containing lead, or certain non-hydrocarbon diesel fuels, should be determined using ISO 39871), which includes a step to produce sulfated ash of higher melting point. NOTE 1 For the purposes of this International Standard, the term “% (m/m)” is used to represent the mass fraction of a material. NOTE 2 With certain types of samples, the test results may not account quantitatively for all the metal compounds capable of forming an ash. Some unused lubricating oils and distillate fuel oils contain metal inorganic additives of low molecular mass (e.g. sodium, potassium), where the metal oxide may sublime below the temperatures specified in this International Standard.