This International Standard specifies a coulometric Karl Fischer titration method for the direct determination of water in crude petroleum. It covers the range 0,050 % (m/m) to 5,00 % (m/m) water in crude petroleum containing less than 0,05 % (m/m) but more than 0,005 % (m/m) of either mercaptan sulfur or sulfide ion sulfur or both. It covers the range 0,020 % (m/m) to 5,00 % (m/m) water in crude petroleum containing less than 0,005 % (m/m) of either mercaptan sulfur or sulfide ion sulfur or both. NOTE 1 A number of substances and classes of compounds associated with condensation or oxidation-reduction reactions interfere in the determination of water by Karl Fischer titration. However, the only likely interfering substances present in crude petroleum are mercaptans and ionic sulfides and providing that they are present at levels less than 0,05 % (m/m), the interference is insignificant when determining water in the range 0,050 % (m/m) to 5,00 % (m/m). NOTE 2 An alternative procedure is provided in annex B for the direct determination of water over the range 0,05 % (V/V) to 5,00 % (V/V) in crude petroleum containing less than 0,05 % (V/V) of either mercaptan sulfur or ionic sulfide sulfur or both. The limitations under which this alternative volume measurement may be used are listed in annex B. The volume measurement may also be used to determine water in the range 0,02 % (V/V) to 5,00 % (V/V) if the above interfering substances are present at levels of less than 0,005 % (V/V) as either mercaptan sulfur or ionic sulfide sulfur or both. NOTE 3 For the purposes of this International Standard, the terms "% (m/m)" and "% (V/V)" are used to represent the mass and volume fractions respectively