Studies on coal-water slurries (CWSs) have been conducted for many years to replace fuel oil. In this research project, the effect of coal properties on CWSs have been investigated using two Turkish coals of different ranks and a Siberian bituminous coal. Physical, chemical and surface properties of coal samples were determined. Furthermore, adsorption tests were carried out in order to put forward the effect of additive adsorption on the viscosity of CWSs. Viscosity measurements were realized for CWSs of various solid ratios by weight that were prepared using coal samples having mean particle sizes of 19, 35 and 50 mum. (C) 2002 Published by Elsevier Science Ltd.