Quartz crystal microbalance (QCM) is a very useful in situ tool for measuring minute changes of mass of thin surface films with real-time monitoring. The effect of temperature deviation and pressure change, viscosity and roughness loading on the frequency shift were examined by measuring the frequency change of bare QCM under high-pressure CO2. From a contour analysis, the frequency shift from viscosity loading and that from roughness loading were obtained. Frequency shift from viscosity loading was about three to four times larger than that estimated by Kanazawa's equation. The resonator, whose surface roughness was larger than the diffusion length, exhibited a frequency shift from roughness loading. (C) 2003 Elsevier B.V. All rights reserved.