A promising method for cleaning coal involves suspending the finely ground material in water and selectively agglomerating the more hydrophobic and oleophilic components with oil or a hydrocarbon such as heptane. In order to study the effect of coal surface properties and other parameters on the rate of agglomeration, a number of agglomeration tests were conducted in which a batch of coal was agglomerated with either heptane or hexadecane, and the rate of change in the turbidity of the suspension was determined. Two types of bituminous coal were utilized, and the surface properties of each type were varied by exposing the ground materials to air at 150 degrees C for periods ranging from a few hours to 84 hr. Measurements made by means of FT-IR photoacoustic spectroscopy showed that the concentration of oxygen functional groups increased with increasing oxidation time. Furthermore, the apparent rate of agglomeration of either type of coal decreased with increasing oxidation time. Therefore, the rate of agglomeration depended on both the rank of the coal and the extent of oxidation of the coal. The rate was also found to depend on the type of agglomerant and its dosage. While the rate tended to increase in direct proportion to agglomerant dosage, the rate of increase with respect to the dosage fell as the coal became more heavily oxidized.