This study compared various thermal cracking processes for Athabasca oil sand bitumen according to the relationship between vacuum residue (VR) conversion and the product yield for each process, using reported data. The conversion was defined as the fraction of VR that was converted to lighter products. The conventional processes examined were visbreaking, delayed coking, and fluid coking, and the developing processes were high conversion soaker cracking (HSC), heavy to light (HTL), I(Y)Q, Eureka, and supercritical water cracking (SCWC). HSC and SCWC were higher severity visbreaking-type processes with conversions of 0.49 and 0.390.50, respectively. HTL and I(Y)Q (recycle) were lower severity fluid coking-type processes with a conversion of 0.52. I(Y)Q (once through) and Eureka showed the highest conversions (0.620.68). Supercritical water (SCW) upgrading was operated experimentally at higher severity, with a conversion of 0.64, and showed the highest yield of distillate product (DP) among all thermal cracking processes investigated. Analysis of the conversionyield relationship revealed the thermal cracking behavior of Athabasca bitumen. The key for achieving higher conversions with lower coke yield was considered to be efficient mass transfer of the volatile fraction stripped away from the condensed phase, which is a liquid fraction at the experimental condition. The condensed-phase decomposition showed an upper limit of conversion of 0.55, and that with a high mass-transfer system exceeded 0.65.