The time-dependent thermal conversion of vacuum residue deasphalted oil was studied at 280, 320, 360, and 400 degrees C. The vacuum residue deasphalted oil was an industrial product produced by vacuum distillation of Athabasca bitumen followed by solvent deasphalting using n-pentane. This type of visbreaking process was of interest for partial upgrading of bitumen to facilitate pipeline transport. Practically useful cracking conversion and viscosity reduction for upgrading were found only at 360 and 400 degrees C. The viscosity measured at 40 degrees C could be reduced by 3 orders of magnitude from 3720 Pa s in the feed to 2-5 Pa s in the product. The density of the product was not reduced by much, despite vacuum residue cracking conversions of 34% at 360 degrees C and 45-47% at 400 degrees C before the onset of coking. The liquid yield was 88-89%. A heavier product fraction was formed during thermal conversion. The heavy material was not necessarily asphaltenes, but an increase in n-pentane-insoluble material was also found that appeared correlated with the aromatic hydrogen content of the product. The limited change in density was at least partly explained by the increase in both heavy material and aromatic nature of the product. Vacuum residue conversion at 360 degrees C increased linearly with time, which indicated zero-order kinetics. Vacuum residue conversion at 400 degrees C was non-zero-order. This study showed that thermal cracking at 360-400 degrees C is better described by a rate equation with two terms. Temperature-dependent differences in the maximum conversion before the onset of coking and the kinetic description of vacuum residue conversion indicated that the equivalent residence time description of visbreaking was an inadequate approximation of thermal conversion at 400 degrees C and below.