The use of a quartz crystal microbalance (QCM) to determine the viscosity of CO2-expanded (CX) liquids was evaluated. This study presents a calibration method for QCM to be used for viscosity measurements at elevated hydrostatic pressures, taking into account the effects of hydrostatic pressure and surrounding fluid density on the resonant frequency of the QCM in an effort to isolate the effect of viscosity. The viscosity values obtained for CX fatty acid ethyl esters and CC ethanol with increasing pressure using the QCM were lower compared to literature data, indicating that the no-slip boundary condition between the QCM surface and the CX liquid was compromised. Thus, a QCM was found not to be suitable for measuring viscosity of CX liquids but could be used to determine the viscosities of gas-free liquids at ambient and elevated pressures. (C) 2015 Elsevier B.V. All rights reserved.