Abstract: The method for processing heavy hydrocarbon feedstock, predominantly heavy crude oil, comprises pre-treatment of an initial feedstock and an auxiliary gaseous mixture at a pre-set pressure, introducing the pre-treated auxiliary gaseous mixture into the pre-treated feedstock and mixing thereof, cavitation treatment of the resulting mixture, separating liquid and gaseous products followed by isolating the final petroleum product. The novelty is in that gaseous hydrocarbons having the activation energy comparable with the molecule dissociation energy of the main components of the heavy hydrocarbon feedstock, are used as auxiliary gaseous mixture; and the pre-treatment of the initial heavy hydrocarbon feedstock and the auxiliary gaseous mixture, both of which are in the liquid state, is performed at a pressure which exceeds the saturated vapour pressure of the auxiliary gaseous mixture.