A carrier gas jet is injected into a liquid hydrocarbon material to form a liquid hydrocarbon-gas mixture; flowing the liquid hydrocarbon-gas material through an inter-electrode gap of a discharge chamber, the inter-electrode gap defined by a spaced pair of electrodes, the electrodes being connected to a capacitor; charging the capacitor to a breakdown voltage of the carrier gas; generating a spark discharge in the inter-electrode gap; and recovering a hydrocarbon fraction that includes lower molecular weight hydrocarbons than the liquid hydrocarbon material.