Publisher Summary Waste oil valorization in a refinery must be considered only after having done a complete feasibility evaluation. Wherever the waste oil is introduced, it should not modify the properties of the refinery products, or the normal operations or functions of the rerefining units. Most oil refineries are complex industrial sites characterized by a very large treated tonnage, a permanent operation of a continuous flow of products from desalination and atmospheric distillation upstream to the storage of finished products downstream passing through all the intermediate refining steps, and the necessity of adapting the units' operating conditions to the treated crude to maintain a good level of quality for the finished products. Other priorities include the need to increase the severity of operating conditions of hydrotreatment to produce gasoline, kerosene, and diesel oil from direct distillation or from thermal or catalytic cracking to comply with the standards for sulfur and aromatic compounds. These constraints provide a better understanding of the importance of alternative valorization routes.