Kerogen from Cambrian and Silurian sedimentary rocks (immature to postmature) from North Greenland has been studied by elemental analyses (C and H), X-ray diffraction (XRD) and infrared spectroscopy (i.r.). The change in the kerogen's structure [derived from the width of half height (WHH) of the (002) diffraction] and the content of functional groups (from characteristic absorption bands in the infrared spectra) suggest the following main processes of maturation: elimination of aliphatic CH₂, CH₃ groups (mature zone): elimination of aromatic CH groups [postmature (catagenesis) zone] and rearrangement of C ≠ C bonds [postmature (metagenesis) zone]. The maturity parameters derived from X-ray diffraction (WHH) and infrared spectroscopy (CH/CC-aliphatic/aromatic ratio) are applicable for maturity ranking in the mature to postmature (catagenesis) zones.