The cracking of petroleum vacuum residue and its co-cracking with coal (SC), plastics (PP, BL), and biomass (BG, CL) was studied by means of thermogravimetry, derivative thermogravimetry, and differential thermal analysis in a nitrogen atmosphere. Differential thermal analysis exothermic and endothermic peaks were assigned to different types of phenomena, such as devolatilzation, polymerization, cracking, and condensation. It is found that condensation and polymerization, which are the most likely exothermal reactions predominant in the cracking of coal and bagasse, suggest the presence of light, little reactive/unreactive aromatic molecules. Alternatively, endothermic phenomena, such as distillation, depolymerization, and cracking, predominant in the cracking of petroleum residue and polypropylene, indicate the presence therein of reactive molecules. The enthalpy values of cracking of petroleum residue and its co-cracking with plastics, coal, and biomass were determined with a view to comparing co-cracking process of mixture with those of the individual components. The detailed results obtained are reported.