This paper reports a low-temperature oxidation study of a Victorian brown coal using seven cylindrical wire-mesh reactors of different sizes, with both steady-state and transient methods. The steady-state method enables determination of the critical ambient temperature, above which spontaneous combustion occurs, as a function of the reactor＇s size. These critical ambient temperatures are then used to calculate the low-temperature oxidation kinetics. The transient method is also applied to directly estimate the rate of oxidation by determining the crossing point, when the thermal conduction term near the center of a cylinder becomes zero. The kinetic constants determined from both steady-state and transient methods are then used to estimate the critical thickness of a layer of coal deposit (infinite slab), above which the deposit is capable of spontaneous combustion. The critical thickness predicted from the steady-state method compares well with those from the transient method, particularly at higher temperatures. This paves a way for future testing using the transient method for a more cost-effective assessment of spontaneous combustion of different materials.