This paper shows an application of bomb calorimetry used in the procedure of regeneration of waste industrial mineral oils. Using the treatment here reported a recovery of nearly 50% of the used oils was achieved. Furthermore, the oils so recovered contain concentrations of potentially contaminant elements far below the requirements of the European Union (EU). Generally speaking, it can be said that the used oil treatment is based on the proper combination of two main procedures, namely the addition and mixture of certain chemicals-precipitant, flocculant and demulsifying agents- in a permanently stirred reactor, at high temperature, and the centrifugation of the mixture. This oil, recovered through the technique of oil regenerating, cleaning, and fitness, can be used either as a raw material for the elaboration of new oils or as a fuel to be used for cogeneration of thermal or electric energy. The treatment described is highly remunerative, both as regards to cost -used oil is subject to a low-cost process, especially if compared to its elaboration from raw materials- and as regards to ecology, since it is recycled, thus saving a great amount of raw materials.