Thermal cracking involves the breakdown of large hydrocarbons to smaller hydrocarbons via the scission of carbon-carbon, carbon-nitrogen, and carbon-sulfur bonds. Mild thermal cracking reactions occur between 350 and 450 degrees C and primarily in the liquid phase. A reaction model implementing vapor-liquid equilibrium (VLE) calculations was developed in this work to better represent the reacting system-the liquid phase. The resulting model can be used to determine reaction kinetics in experimental systems that have a VLE component, which would normally make it inadequate for reaction kinetics determination. A mild thermal cracking experimental program was conducted with three crude assays: Hardisty (MBL), Albian heavy synthetic (AHS), and Christina Lake diluted bitumen (CDB). The experiments were conducted in a pilot-scale semibatch vertical reactor with a sweeping nitrogen gas blanket in the head space. The three crude oils were reacted at mild conditions: 350, 400, 425, and 450 degrees C at 1.24 MPa(a). The reaction model with VLE calculations was used to determine reaction rates representative of the experimental data collected. The coefficient of determination between the reaction model's predicted system composition and the experimental data for MBL, AHS, and CDB were determined to be 0.99, 0.99, and 0.98, respectively. Moreover, 80, 85, and 89% of the model's predicted system composition had less than 10% error for MBL, AHS, and CDB, respectively.