The present invention provides a method for decreasing the Conradson carbon ("Concarbon") number of petroleum feedstreams by passing an electric current through a mixture of a petroleum stream, typically having a Conradson carbon residue of at least about 0.1% and an aqueous electrolysis medium at a pH and cathodic voltage for a time sufficient to decrease the Conradson carbon number of the petroleum stream. The electrolysis medium contains quaternary carbyl or hydrocarbyl onium salts; inorganic hydroxides such as NaOH or KOH, or mixtures thereof. A cathodic voltage of 0 V to -3.0 V vs. Saturated Calomel Electrode (SCE) and a pH of 6-14, preferably 7 to 14, more preferably above 7 to 14 are used.The invention has utility for converting less economically desirable refinery feeds to feeds that are more valuable.