The researchers studied different types of coal from the Tertiary Barito region to understand how their quality is influenced by geological factors. They looked at the composition of ten coal samples and found that vitrinite, liptinite, inertinite, and mineral matter are the main components. The amount of liptinite and inertinite in the coals decreases as the vitrinite content increases. The coal from the Palaeogene period is of higher quality compared to the Neogene coal, with higher vitrinite reflectance indicating a higher rank. The slight change in reflectance from top to base is due to thicker cover on high-rank coals. The type and quality of the coals are influenced by the geological setting where they formed.