We show that both chemical and physical changes induced in Victorian brown coal through thermal processing in the presence of a range of gases has a profound effect on its oxidation behavior. In particular, the appearance of a low-temperature DTA peak which is believed to be related to the propensity of the coal to spontaneously combust is strongly correlated with the extent of the pore surface as determined by the fractal surface measure obtained from small-angle X-ray scattering measurements.