Pyrolysis of heavy organic resources follows the radical mechanism. It involves the reactions between radicals generated from the cleavage of covalent bonds in a reactant and the reactions between the radicals and the reactant. The radicals are the reactive intermediates that govern the rate and product distribution of pyrolysis. This paper quantifies the reactive intermediate radicals generated in direct pyrolysis of two n-alkylbenzenes and the induced pyrolysis of the alkylbenzenes by the radicals, based on the data obtained in pyrolysis with and without tetralin that is able to donate hydrogen radicals. It is found that about 90% reactive intermediate radicals can be capped by the hydrogen radicals from tetralin. At 400-440 degrees C the contribution of induced pyrolysis is more than that of direct pyrolysis, about 1.9 times for n-propylbenzene and 3 times for n-pentylbenzene. The role of induced pyrolysis is larger at higher temperatures due to its higher activation energy than direct pyrolysis.