Coal-water mixtures (CWM) are concentrated suspensions of coal particles in water. The rheological properties of CWM depend on a number of factors such as the type of coal, the solid content and its size distribution, the temperature, the pH and the presence of electrolytes and chemical additives. The slurry viscosity was influenced significantly by initial surfactant loading, the particle size distribution and the ash content of the feeds. CWS of up to 60% prepared from Bickershaw coal samples with low ash contents (4.0% and 6.86%) could be produced at acceptable viscosities in the presence of a non-ionic surfactant, Triton X-405. To produce pumpable slurries with more than 60% solid, it will be necessary first to achieve a significant level of demineralisation, and to use high levels of reagent addition. The viscosities of the slurries with low ash content were significantly reduced by the surfactant addition which also altered the rheological characters of these slurries from non-Newtonian towards Newtonian fluids. However, sample containing very fine particles with a high ash content (24.5%) showed non-Newtonian behaviour even in the presence of reagent.