Fixed-bed hydropyrolysis of petroleum source rocks and low-rank coals at pressures of ca. 15 MPa in the presence of a dispersed sulfided molybdenum catalyst gives rise to extremely high oil (dichloromethane-soluble) yields (>60%) with overall conversions of the organic matter typically being greater than 90%. To ascertain whether hydropyrolysis oils are representative structurally of their parent kerogens, carbon skeletal parameters derived from their solution state 13C NMR spectra have been compared with those from the quantitative solid state 13C NMR analysis conducted using the single pulse excitation (SPE) technique on type I, II, and III kerogens. Indeed, when the latter values are corrected for carboxyl/carbonyl carbons, both the carbon aromaticities and long alkyl chain contents of the hydropyrolysis oils and the parent kerogens investigated, within experimental error, are similar. This indicates that catalytic hydropyrolysis does not involve a significant change in aromaticity, unlike in normal pyrolysis where the extent of aromatization for type I and II kerogens is considerable. For the hydrogenation and dehydrogenation that do occur, the extents of reaction must be fairly similar to keep the overall aromaticity constant.