A new Couette-type high-temperature, high-shear-rate viscometer capable of performing viscosity measurements at high temperatures (up to 150 °C) and high shear rates (up to 3 × 106 s−1) has been designed, developed and constructed at Koninklijke/Shell-Laboratorium, Amsterdam, the Netherlands. This paper highlights the important design and constructional aspects and modes of operation of this instrument, which has special features in terms of operational range, ease of experimental procedure, access to primary experimental quantities (such as gap width and oil film temperature) and data handling technique. It also describes the calibration of the new instrument and a first series of measurements with non-Newtonian CEC reference oils at temperatures of 100 °C and 150 °C and shear rates up to 3 × 106 s−1. The latter results agree very well with those obtained by other workers employing different viscometers. The new viscometer has proven to be very suitable for the accurate determination of the rheological behaviour of engine lubricants at high temperatures and high rates of shear.