This International Standard specifies a method for determining the amount of carbon residue, in the range of 0,Ol % (m/m) to 30,O % (m/m), left after evaporation and pyrolysis of an Oil, and is intended to provide some indication of relative Coke-forming tendency. The method is generally applicable to relatively non-volatile Petroleum products which partially decompose on distillation at atmospheric pressure. NOTES 1 The term “carbon residue” is used throughout this International Standard to designate the carbonaceous residue formed during evaporation and pyrolysis of a Petroleum product. The residue is not entirely composed of carbon, but is a coke which tan be further changed by pyrolysis. The term “carbon residue” is retained in this method only in deference to its widespread use. 2 The carbon residue of distillate and residual fuel oils gives an approximate ranking of such fuels in terms of their propensity to form deposits in specific applications. 3 The presence of alkyl nitrates in distillate fuels, or ashforming additives in either distillate or residual fuels, will give carbon residue results that are higher than the corresponding values of the fuel without additives. These values may not correlate with the propensity of a fuel to form deposits. 4 The carbon residue of base lubricating oils may give an indication of the propensity of the oil to lay down deposits in combustion chambers, and/or of the relative Chemical constitution of oils of similar viscosity. Most finished lubricating oils contain ash-forming additives, and thus the carbon residue of finished lubricants cannot be used in this manner. 5 The carbon residue of a gas oil is a useful guide in the manufacture of gas.