The performance of a high pressure failing sinker-type viscometer has been evaluated both by experiment and by CFD and is, for the first time, such an evaluation has been reported. This type of viscometer is used to determine the viscosity of liquids at high isostatic pressure. By assuming the existence of fully developed laminar flow between the descending sinker under the influence of gravity and the tube wall, an analytical solution to flow can be determined. However, due to end effects, a calibration fluid is required to correct determined viscosity data. Using an edible oil as the test fluid, we examined the flow profile around the sinker during operation. By using CFD we have been able to confirm the presence of complex flow patterns. These are directly responsible for influencing the rate of sinker descent and thus the determination of viscosity data, which highlights the need for good sinker dimension selection as well as the need for calibration. (C) 2007 Elsevier Ltd. All rights reserved.