Density separations of six world coals have been carried out. The coals were provided as pf samples and were screened to provide size fractions at -38 + 20 mu m from which tight density fractions (0.02 and 0.03 g cm(-3) intervals) were produced in a heavy liquid medium using the float-sink procedure, Each density fraction was characterised by manual maceral analysis and a new automated image analysis technique called the reactivity assessment program. The chemical structure of each fraction was examined by C-13 n.m.r. and FT-i.r. spectroscopies. The reactivity of the density fractions was assessed using a drop tube furnace at a temperature of 1300 degrees C, residence time of 100 ms and 1 vol% oxygen atmosphere, The morphology of the chars produced in the drop tube furnace were examined manually and using an automated image analysis technique. This allowed the predicted reactivity of the fractions to be correlated against actual burnout characteristics.