To obtain an insight into behavior of saturated components in thermal cracking of heavy oils, Curiepoint pyrolysis of mixtures of aromatics (A) and polar compounds (P) fractions (A+P) of deasphalted oils (DAO) (i.e. DAO samples not containing saturates fraction) prepared from an Arabian mixture (AL/AM) and Minas crude was examined in the presence of three kinds of saturated model compounds, triacontane, squalane, and cholestane. It was found that the naphthenic compound, cholestane, can considerably reduce coke yields from both oil samples, whereas the other two compounds showed essentially no effect. Possible role of naphthenic compounds in the thermal treatment of heavy oils was also discussed, based on the results of the pyrolysis of cholestane. In addition, pyrolysis of asphaltenes from the two crudes, in the presence of the saturates fraction of AL/AM-DAO, which contained a relatively large amount of naphthenic compounds, was also examined.