Adiabatic oven testing of seven coal samples with a similar rank has been conducted, which demonstrates differences in their self-heating rate behaviours under the mine settings that they are found in. This has been achieved using a new benchmarking adiabatic test that provides an accurate means of establishing if a coal can reach thermal runaway and in what minimum timeframe. Four of the samples reached thermal runaway, but there was a considerable range in the time taken. The shape of the self-heating rate curves also showed a degree of variation. One of the samples displayed gradual self-heating over the duration of the test and would have reached thermal runaway eventually. The other two samples initially self-heated and reached a maximum temperature before the heat loss mechanism from moisture evaporation dominated and the coal temperature steadily decreased. One of these samples was retested at a lower moisture state and was able to reach thermal runaway. These results confirm the importance of testing samples to assess the risk of developing a spontaneous combustion event.