Residual oil from the processing of crude oil, natural bitumen or oil sand is mixed in a mixer with granular, hot coke as heat carrier (heat carrier coke) in a weight ratio of 1:3 to 1:30, where on the granules of the heat carrier coke there is first of all formed a liquid residue film which partly evaporates in the mixer. Gases and vapors and moist, sticky coke are withdrawn from the mixer. The mixture of coke and residual oil is introduced into a subsequently connected stirred tank in which the mixture slowly moves downwards while being stirred mechanically at a temperature of 450 to 600° C. and preferably at 480 to 550° C. Dry, flowable coke is withdrawn from the stirred tank. Usually, the dwell time of the heat carrier coke in the stirred tank is 1 to 30 minutes.