Two Spanish bituminous coals, wet, preheated, oxidized and post-maturation have been studied by quantitative FTIR spectroscopy. Comparative evolution of H/C and O/C atomic ratios have been considered in a van Krevelen diagram. Results from FTIR indexes indicate that coal preheating is responsible for a decrease of aliphatic groups. Structural changes during oxidation are affected by previous coal preheating. The behaviour of these materials during artificial maturation reveals a different hydrocarbon potential for wet, preheated and oxidized coals.