Oxyreactive thermal analysis (OTA) carried out in the conditions of full access of oxygen to each reacting particle of the sample investigated is a suitable method for the determination of important properties of the organic matter dispersed in the rocks. Its results may be easily evaluated to the form of values to be used in a clear diversification and classification system of organic matter/kerogen, as well as to the evaluation of its transformation process in a rockmass. The OTA also enables the distinguishing of the transformation stages and the investigation of the results of the gaseous products liberation from organic matter and kerogen. The OTA method may be applied as a complementary one for the Rock Eval analysis and be used for the organic geochemical and bituminological studies for geological bitumen prospecting.