Hydrogen donor reactions in the coprocessing of coal and petroleum resids have been investigated using different hydrogen-rich model compounds and reduced resids as donors and aromatics as accepters. Three hydrogen-rich donor species were compared : cyclic olefins, hydroaromatics, and cycloalkanes; the aromatic accepters included pyrene and anthracene; and the resids were reduced by a modified Birch method. Hydrogen was transferred at 380 degrees C most readily by cyclic olefins, followed by hydroaromatics, and the least by cycloalkanes. Catalysis by thiophenol promoted hydrogen transfer by the cycloalkanes at 380 degrees C but had little effect at 440 degrees C. Reduced resids transferred substantially more hydrogen to an aromatic acceptor than did the parent resids. In a ternary system of resid, cycloalkanes, and aromatic, the reduced resids yielded more hydrogen transfer and promoted hydrogen donation from the cycloalkanes in a nitrogen atmosphere. Reduction of resids by the Birch method appeared to be an effective means of increasing the hydrogen donor ability of resids,