Diverse coke deposition mechanisms and models, all supported by experimental data, have been proposed for catalytic hydrogenation processes related to heavy oil and bitumen refining. In this contribution, nanofiltration is used to partition Athabasca bitumen and Maya crude oil so that the potential impact of asphaltene-rich nano-aggregate size on coke deposition on a commercial NiMo/gamma-Al2O3 hydrotreating catalyst could be investigated without introducing artifacts related to the use of solvents. Crude samples were filtered at 473 K through 5, 10, 20, and 50 nm ceramic filters. The feeds, permeates, and retentates are characterized in detail in a companion contribution (Zhao and Shaw, Energy Fuels 2007, 21 (5), 2795-2804). Batch coking experiments were conducted at 653 K for 2 It at a 30:1 feed to catalyst ratio (weight basis), with feed stocks, permeates, retentates, and control samples. Surface area, pore volume, and pore size distribution of coked catalysts were measured. The results were found to be consistent with partial filling of catalyst pores for all cases. Pore mouth plugging was not observed. Elemental analyses performed on cross sections of coked catalyst pellets show that coke deposition within pellets was diffusion limited for all cases evaluated while vanadium deposition, arising primarily from the maltene fraction, was not diffusion limited. Asphaltene-rich nano-aggregate size and maltene composition are shown to play secondary roles in coke deposition within catalyst pellets.