Dynamic tube blocking tests have been conducted to determine the effect of increasing temperature and pressure on barium sulphate and calcium carbonate scale formation, as part of a study considering the application of scale inhibitors in high pressure and high temperature reservoirs. As pressure was increased, the scaling tendency of the carbonate and sulphate scaling brines tested was found to decrease, as was predicted by scale prediction software. As temperature was increased, the scaling tendency of the carbonate scaling brine increased, whereas that of the high sulphate scaling brine system was found to decrease. The effect of temperature on scaling tendency was more significant than that of pressure. A low sulphate scaling brine was also tested and this failed to precipitate scale during the tests at the lowest temperature (50 C), although at this lowest temperature, it was predicted to have the highest scaling tendency. Under these test conditions, the kinetic rate of scale precipitation was low, so the kinetic rate of precipitation became more significant relative to the thermodynamic drive for precipitation. © 2002 Elsevier Science B.V. All rights reserved.