Kerogen has been found to have a wide range of composition and chemical structure. Molecular representations of kerogen from Green River shale were first constructed by . The basis of the model was the structure of the chemical degradation compounds of kerogen and accounted for features observed in X-ray Diffraction (XRD), Infrared (IR), and electron spectroscopy measurements. The model had a bulk formula of C235H397O13N3S5. Siskin et al (1995) later developed a model for kerogen by incorporating evidence from solid state 13 C NMR in addition to mass spectrometry analysis of pyrolysis products of kerogen. Molecular model for kerogen at different stages of thermal maturity was given by Behar and Vandenbrouke (1986) which shows an increase in aromatic chains in later stages of thermal maturity. Kerogen from green river shale was found to contain carboxyl, ester, amide, hydroxyl, aldehyde, and ketone groups (Fester and Robinson 2009). suggests that as the metamorphic degree increases, the the carboxyl and hydroxyl functional groups undergo major changes while the carbonyl groups tend to remain the same.