A continuous process for the thermal treatment of a refinery sludge, comprising the following operations: a. drying of the refinery sludge, possibly mixed with pet-coke, at a temperature ranging from 110 to 120° C.; b. gasification of the dried sludge, at a temperature ranging from 750 to 950° C., for a time of 30 to 60 minutes, in the presence of a gas containing oxygen and water vapour, with the associated production of synthesis gas (CO+H2) and a solid residue; c. combustion of the synthesis gas at a temperature ranging from 850 to 1,200° C. and recycling of the combustion products for the drying and gasification phases; and d. inertization of the solid residue, at a temperature ranging from 1,300 to 1,500° C., by vitrification with plasma torches.