In extraction. treatment of the 470C-EP cut of heavy vacuum gasoil with a mixture of N-methylpyrrolidone and octane, the carbon residue of the gasoil decreases from 4 to 1.75 wt. %. In catalytic cracking of such treated feedstock, the relative yield of naphtha and diesel cuts increases by 10 and 37% and coking decreases by 30%.