Recent interest in producing superclean coal has lead to the development of coal cleaning techniques which require the grinding of coal to sizes below 10 microns. Coal in this size range has inherent material handling problems, most of which can be eliminated by the utilization of this ultrafine coal in a slurry form. Ultrafine coal-water slurries, prepared from an Eastern bituminous coal, are investigated to determine the effect of size distribution on slurry rheology. The effect of reagent addition on slurry rheology is normalized by conducting experiments at optimum additions determined to maximize particle dispersion. As a result of this investigation, it has been found that the maximum solids loading for ultrafine coal slurries ranges from 55 to 60 percent by weight as compared to 70 to 75 percent solids reported for coarser slurries. It was further shown that as particle size decreases there is an increase in slurry viscosity and a corresponding decrease in maximum solids loading. Continued analysis in view of a suspension viscosity model (Lee, 1970) yields unsatisfactory predictions as compared to the experimental results. Modification of this model by incorporating a volume correction factor improves the correlation between model predictions and experimental results. The volume correction factor reflects an increase in apparent solids loading which becomes greater as the particle size decreases. Also investigated is the effect of various reagents on the rheology of ultrafine coal slurries. Pseudoplastic or dilatant slurry rheologies are shown to be more dependent upon dispersing reagent than the size distribution. / M.S.