The effect of hydrothermal factors in a flow system on the character of transformation of asphaltenes from bitumens and crude oils of different chemical types has been studied by instrumental methods. It has been shown that hydrothermal treatment results in degradation of the aliphatic moiety of asphaltene molecules, yielding alkanes, alkenes, phthalates, and other compounds; it also results in washout of high-molecular-mass petroleum components associated with asphaltenes, thereby leading to the structuring of asphaltenes in the line of their carbonization and to enhancement of their paramagnetic properties. Independently of the chemical type of bitumen or crude oil, asphaltenes lose their solubility in benzene after hydrothermal treatment and become similar to carbonized compounds of the carbene-carboid type.