Coagulation of asphaltenes in crude oil has been studied by 1 electronic spin resonance (ESR). Free radicals in asphaltenes with the content of vanadium less than 0.1 mass% are found to recombine when asphaltenes precipitate. Polyaromatic fragments are shown to be localized in the inner part of the asphaltene molecules. A possibility of the formation of diamagnetic compounds between vanadyl (VO2+) complexes and free radicals of asphaltenes is investigated.