A new model is developed for predicting the effective thermal conductivity of regularly packed beds of rough, uniformly sized spheres immersed in a stagnant gas. Contact mechanics and thermal analyses are performed and the results are presented in the form of compact relationships. The present model accounts for the thermophysical properties of spheres and the gas, load, the rarefaction effects of the interstitial gas, gas temperature and pressure, and spheres diameter, roughness and asperities slope. The present model is compared with experimental data with the sphere diameter of 19.05, 25, and 50.4 mm and good agreement is observed. (c) 2006 Elsevier Ltd. All rights reserved.