This standard specifies a method for characterizing the flow properties of non-solid surfactants, alone or in the form of mixtures, as well as products consisting essentially of surfactants, using a rotating viscometer with coaxial cylinders, with cone and plate, with double cone, etc. NOTE- The rheological behavior of a system containing surfactants is frequently affected by anomalies. In most cases, these are due to the tendency of surfactant molecules to form associations. The rheological behavior of surfactants depends essentially on their nature and their concentration. Small variations in temperature, in the concentration of mineral salts and in the presence of any other substance, can also modify the rheological behavior of surfactants. In certain cases, these variations change the type of rheological behavior. The method specified in this standard attempts to take into account all the observations indicated above. For certain types of very special surfactants, other determination methods can be used. For Newtonian systems, the methods used in rubber latex and liquid petroleum products are suitable (see annex). When the Newtonian behavior of a system is not evident, the method specified in this UNE standard allows choosing the appropriate measuring device to determine the real rheological behavior.