Certain North American subbituminous rich in the maceral inertinite have been associated with high carbon loss in pilot plant and full-scale combustion systems. This experience has been interpreted to mean similar experiences which may be expected to occur with Southern Hemisphere coals known to be rich in inertinites. As a first step in the process of assessing the impact of inertinites on the combustibility of coal, samples of various rank coal obtained from various geographic locations including North America, Australia, Africa, and China were examined petrographically and subjected to thermal analysis. Quantitative evaluation of the thermoanalytical combustion profiles indicate that the inertinites are indeed slightly more reactive than vitrinite. A reduction in reactivity is primarily a function of coal rank and its associated properties, i.e, volatility, vitrinite reflectance, O/C ratio and H/C ratio.