A high pressure viscometer is described capable of measuring viscosities over the range 1 to 104P at pressure to 3500 kg/cm2and at temperatures between −60° and 100°C. The device is constructed from commercial high pressure tubing and is mounted in a commercial thermal air bath. Calibration is made at atmospheric pressure with the liquid under test against a series of Canon‐Fenske viscometers. Accuracy of the measurement is better than 1% at all viscosities in the range of the device.