Pyrolysis is an environmental and economical process, through which fuel oil may be obtained and waste polymers may be recycled. However, the carbon deposition, which forms to depths of several mm, reduces heat transfer and limits operation time and decreases the reactor efficiency by way of corrosion and oxidation of the reactor. In this study, experiments were focused on examining how the carbon deposition is generated in the continuous pyrolysis reaction by feeding base lubricating oil, lubricating oil and waste lubricating oil. Moreover, effects of minerals, reaction temperature, additives and feeding rates on carbon deposition were examined. Zinc and calcium increase the coke formation, but sulfur additives in feed suppress the carbon deposit. Iron material in the pyrolysis reactor shows that coke formation increases with iron oxidation.