An immature humic coal (subbituminous rank) from the Mahakam delta (Kutei basin, Kalimantan, Indonesia) was isothermally pyrolyzed in confined conditions at temperatures ranging from 250 to 400 degrees C (10 degrees C steps) at 700 bar pressure for 72 h. Solid, liquid and thermodesorbable phases originating from the pyrolyzates have been analyzed by different analytical techniques. Results indicate that a 10 degrees C pyrolysis step is necessary to determine the timing and the sequence of the different transformations affecting the kerogen as well as the effluents. Four maturation/coalification stages are distinguished. Stage 1 (75-80 wt.% C) occurs when modifications mainly concern the oxygen-bearing functions of the kerogen. Stage 2 (82-85 wt.% C) is characterized by the decrease of the aliphaticity and the primary cracking of the coal. Stage 3 (86-89 wt.% C) corresponds to the production of methane and the condensation of aromatic rings in the solid residue.