We pyrolyzed long-chain, polycyclic, n-alkylarenes with varying amounts of different polycyclic arenes and methylarenes to investigate hydrogen transfer and hydrogenolysis in these systems. The addition of 1-methylpyrene enhanced hydrogenolysis in 1-undecylnaphthalenene at pyrolysis whereas the addition of 1-methylnaphthalene had no such effect. The addition of 1-, 2-, and 9-methylanthracene, 1-methylpyrene, and anthracene enhanced hydrogenolysis in 1-alkylpyrene pyrolysis, whereas the addition of methylnaphthalenes, naphthalene, phenanthrene, and pyrene had no such effect. These results are consistent with arenes serving as hydrogen shuttlers and methylarenes serving as both hydrogen donors and hydrogen shuttlers. Dewar reactivity numbers, which are a measure of the localization energy in aromatic systems, can be used to assess a compound’s propensity for hydrogen shuttling and hydrogen donation. These results indicate that the structures of the polycyclic moieties in a heavy hydrocarbon feedstock can strongly influence hydrogen-transfer reactions and subsequent hydrogenolysis. The results also imply that effective hydrogen shuttlers could cause more of the hydrogen present in heavy oils or resids to be used to break C-C bonds. Thus, there may be opportunities to manipulate thermal hydrogen-transfer reactions during the conversion of heavy oils and residua.