With the discovery of an ubiquitous deep biosphere on Earth inevitably the question on its potential carbon and energy sources arises, therefore, several studies have been carried out to prove that organic carbon rich lithologies like lignites, coals and kerogen could act as potential “feeder” lithologies for the deep biosphere, leading to the deduction that abiotically driven degradation reactions of the buried organic matter will provide substrates, such as water – soluble low molecular weight organic acids (LMWOA), for microbial activity in deep sediments. However, the rates and quantities of this process still have to be elucidated. With this in mind, research is focussed to characterise the water soluble organic compounds of different organic-rich sediment and rock samples, like e.g. a sequence of samples representing early diagenesis, a maturity sequence of coals and other source rocks and a sequence of biodegraded reservoir rocks. The samples will be analysed for mapping of feedstocks in the C2 to C10 range, providing insights into the influence of diagenesis, maturity and biodegradation on the availability of low molecular weight substrates and developing a new methodological approach in GC-IRMS for organic acids.