The optimization of coal-bitumen coprocessing would be facilitated by a quantitative measure of the amount of coal incorporated into all the individual product fractions. Intrinsic C-13/C12 ratios of coal and bitumen are sufficiently different that they can be used as tracers to this end by applying isotopic mass balance. However, thermal treatment may cause isotopic fractionation in bitumen and coal complicating the application of a simple mass balance. To minimize this effect, mild experimental conditions were chosen for this study. Also, isotopic fractionations induced in bitumen by processing at these conditions were determined and used to correct mass balance calculations for the concentration of dissolved coal in product. The effect on coal solubilization of coal loading, catalysts and presence of coal ash was investigated. Also the fate of coal dissolved in distillate from coprocessing was traced through further secondary hydrotreatment. (a) Concentration of coal in the initial charge influenced the proportion of coal and bitumen in the product fractions. The yield of distillate from both coal and bitumen, and the yield of pentane soluble product from the coal were relatively independent of the size of the initial coal charge; however, distinct relationships were observed among the other fractions. (b) Different elements doped to iron oxide affected coal and bitumen transformation differently. Effective iron based catalysts for coprocessing that left minimal toluene insoluble residue from coal were Fe2O3, Fe2O3/TiO2 and a sludge from nickel refining. (c) Coal ash was shown to improve coal solubilization. (d) Dissolved coal was preferentially concentrated into light oil after secondary hydrotreatment of coprocessed distillates.