Three vacuum residual oils (VR) derived from Ratawi Burgan (RB), Lower Fars (LF), and Eocene (EOC) crude oils were subjected to thermal cracking in a pilot plant, which simulates the Eureka process, to produce cracked distillate petroleum products and residual pitch. The cracking reaction was performed at 430 degrees C for 50 min. The chemical composition of the produced cracked petroleum products and byproduct pitch was studied to determine its relationship to the variations in the properties of the feedstock. Saturates, aromatics, resins and asphaltenes (SARA) analysis of the vacuum residues, cracked oils, and pitch show that the residues and pitch consist mainly of aromatic hydrocarbons (VR: 94 wt %; pitch: 99 wt %), while the oils themselves contain about 42 wt % saturated hydrocarbons (oil(RB): 46 wt %; oil(EOC): 44 wt %; oil(LF): 36 wt %). H-1 and C-13 NMR revealed that the VRs consist predominantly of alkyl aromatics with di-, tri- (aromatics, resins), and polyaromatic rings (asphaltenes) that thermally decompose splitting the molecules into saturated lower molecular weight hydrocarbons and aromatics having lower aliphatic carbon attached to it. Regardless of the feed, all oils contain more aliphatic (similar to 62 wt %) than aromatic carbon (similar to 21 wt %). The cata-condensed aromatic moiety in the oil is triaromatic. The effect of feedstock on the chemical composition of the oil and pitch is most prominent for the aromatic and asphaltenic fractions.