The application of molten caustic leaching, MCL, for the desulphurization and ash removal from delayed and fluid oil sand coke residues has been studied at a temperature of 400-degrees-C. The variables studied were sodium hydroxide to coke weight ratio (1.0-2.0), reaction time (0-2 h) and coke washing conditions. The results obtained indicate that both coke samples were amenable to molten caustic leaching. The optimum reaction time for desulphurization and ash removal for both cokes at 400-degrees-C was determined to be 30 min. It is shown that the desulphurization conditions that will concurrently give high carbon recoveries correspond to a desulphurization index of 80% for both coke residues.