This paper reports results from an experimental study on low-temperature oxidation of a bituminous coal in an isothermal flow reactor. The rates of consumption of oxygen and the formation of carbon oxides were quantified by an on-line oxygen analyzer and a dual-column micro GC. Water produced during oxidation was measured using a drierite absorber. This allowed detailed calculations of mass balance during the oxidation experiments. It is observed that the rates of oxygen consumption and the formation of carbon oxides decreased with time, as opposed to the mass of coal sample, which tended to increase during the experiments. The integral amounts of gaseous products evolved in each experiment indicate that CO2 production is far larger than that of CO and the molar ratio among H2O, CO2, and CO production is about 21:3;1 at the present experimental conditions. It is proposed that the molar ratio of produced CO to consumed O-2 be applied as an index for ranking coal propensity to self-heating and for determining the; onset of spontaneous combustion.