The influence of rapeseed oil additives to oil tar on the results of thermal cracking is studied. In the mixing of oil tar with rapeseed oil, the change in the yield of cracking products is found to be nonadditive. The composition of cracking mixtures is investigated as a function of the amount of rapeseed oil introduced into oil stock. We also show the fundamental possibility of integrating thermal processing of plant oils into the technological structure of oil refineries.