Open system non-isothermal (programmed) pyrolysis experiments have been conducted to investigate the pyrolytic liberation of molecular hydrogen (H-2) and methane (CH4) from carbonaceous shales and coals of different rank and organo- and lithofacies types. The aim was to explore the origin and generation pathways of H-2 and their relation to methane generation mechanisms. The experiments were performed at two heating rates (0.5 and 1 degrees C/min) up to a final temperature of 1200 degrees C. CH4 and H-2 generation usually did not proceed simultaneously but with a distinct temperature offset Molar yields of H-2 under open system pyrolysis conditions were always considerably higher than the corresponding CH4 yields. While coaly material showed one single, broad H-2 generation peak. H-2 evolution from shales revealed complex release patterns. The pyrograms (gas generation rate as a function of temperature) were classified according to the number and shape of peaks and the maximum temperatures of the main phases' gas liberation. H-2 pyrograms were tentatively subdivided into five groups (A-E) according to peak patterns, reflecting different thermal stabilities of precursor moieties. Based on previous research on H-2 generation mechanisms, different evolution pathways are proposed to explain the observed H-2 release patterns. For shales, the dominant mechanism shifts from cracking of hetero-bonds and demethylation in Group A towards aromatization and condensation in Groups B and C. In coals, aromatization and condensation are considered to be the predominant H-2 evolution mechanisms. The molar yields of H-2 correlate like the CH4 yields with the TOC and Rock-Eval S2 values of the samples, indicating a purely organic origin. The results have implications for hydrogen balance considerations during thermal maturation of coals and gas/oil shales. (C) 2014 Elsevier B.V. All rights reserved.