The method is applicable when an agreement has previously been reached between the interested parties for the removal of two representative samples during filling of the tank-wagon at the manufacturer's premises. It cannot be applied when it is intended to determine the water content. The principle consists in checking that the equipment used is gas-tight; collection of the samples in steel bottles. One bottle is intended for the customer and the other is retained by the manufacturer in case an analysis is required for checking purposes. - Replaces ISO Recommendation R 1552-1970.