Reaction products by the reactions at 50°C between DPPH and hydroaromatics in the presence of oxygen were investigated, and the following results were obtained(1) Octahydrophenanthrene (OHP), synthetic H/D (derived from coal, multi-component, effective toward deteriorations of hydrocarbon products) and HHAP (derived from petroleum, multicomponent, effective toward deteriorations of hydrocarbon products) exhibited greater radical scavenging abilities than tetralin.(2) The formation of N, N-diphenyl-N'-picrylhydrazine (the hydrate of DPPH) was confirmed.(3) In the case of the addition of tetralin, about 20% of the disappearance of hydrazyl radicals is attributive to the dehydrogenation of tetralin, but about 80% of that can be supposed to be attributive to the oxidation products from tetralin. However, in the case of the addition of OHP, 98% of the disappearance of the radicals can be attributed to the dehydrogenation of OHP.From these results, OHP can be thought to behave differently from tetralin in the presence of oxygen, and these results can support the previous experimental results that the deteriorations of the hydrocarbon products are inhibited by hydroaromatic type inhibitors.