A rudimentary capillary‐type viscometer for measuring viscosities between 103and 1010poise at high pressures is described. Measurements are reported on petroleum ether to 57 kbar where the viscosity is approximately 1010poise and on a 1:1 mixture ofn‐pentane‐isopentane to 54 kbar where the viscosity is approximately 106poise. Measurement precision of the technique is a few percent, but uncertainty in absolute determination at maximum pressure is only within a factor of two. Viscous stresses are shown to decay exponentially with time even at the highest pressures, and no effects of residual stress are observed.