The characterization of the microbial ecology of three different Spanish coals was performed to isolate microorganisms suitable for biodesulfurization processes. Some of the isolated microorganisms were identified, using phenotypic and genotypic properties, as species of different genera: Cryseomonas, Xanthomonas, Pseudomonas, and Moraxella. The biodesulfurization capability of various isolates at different conditions were compared to those obtained with native mixtures of microorganisms. The B12 isolate produced important values of desulfurization at 30 degrees C.