The generation and decay of free radicals upon photoirradiation in the major components of catalytically cracked heavy gas oil were studied by ESR spectroscopy. It was shown that the concentration of radicals decreased in asphaltenes after photoirradiation, unlike the case of hydrocarbons and resins, in which a radical buildup was observed. Tentative mechanisms for the generation and decay of paramagnetic species in heavy catalytic gas oil are discussed.