The heavy oil obtained from the distillation of the pyrolysis oil obtained from the vacuum pyrolysis of used tires was incorporated into different rubber formulations to investigate the possibility of using the oil as a plasticizer Promising preliminary results obtained by comparing a pyrolytic oil (IBP > 204 degrees C) with the commercial aromatic oil Sunder 790 (IBP > 344 degrees C) and studying a the plasticizing action of both oils in rubber compounds, prompted us to carry out a more detailed study with a heavier pyrolytic oil (IBP 240-450 degrees C). The latter was compared with the commercial aromatic ail Dutrex R 729. Several formulations were prepared with varying percentages of either the pyrolytic oil or the commercial oil. The results indicated that the heavy pyrolytic oil demonstrated good mechanical and lubricating properties, very similar to the commercial oil.