Two different methods to determine the effective thermal conductivity of six Mexican cementing systems used in geothermal well completion were compared in the temperature range from 28 to 200 degreesC. Measurements were taken using the classical line-source method and the Jaeger method. The experimental thermal conductivity uncertainties were 4% and 11.8% for the line source and Jaeger's methods, respectively. (C) 2003 Elsevier Ltd. All rights reserved.