Abstract: The high shear, high temperature viscometry of non-Newtonian oils requires absolute viscometry or reference fluids from such viscometry to use with relative instruments. To be sufficiently precise, such absolute viscometry should be established at the temperature and shear rate of concern. The authors show how the Tapered Bearing Simulator meets the above criteria of performance. The instrument is then applied to the international reference oils established by the ASTM and CEC and the results seem to indicate that previously generated viscometry values may be in considerable error regarding the apparent shear rate applied.