Abstract: Method for predicting amounts of biogenic gas generated by biological conversion of organic matter deposited in sediments on the geological time scale. Bioreactive structural units having formulae CxHyOvSzNw with x>6, y>x, v<6, z<6 and w<6 are considered. A sample of a rock of the sedimentary series is then taken at a depth close to the surface, such that said rock has not been subjected to any biodegradation, and amounts of each bioreactive structural unit present in this sample are determined. A reaction scheme is defined in which the bioreactive structural units react in parallel with electron acceptors, and each of the bioreactive structural units reacts sequentially with these electron acceptors. Finally, the amount of biogenic gas produced by biodegradation of the bioreactive structural units is determined by means of the reaction scheme and the amounts of each structural unit present in the sample.