Rheological Study of Athabasca Bitumen and Maya Crude Oil MD. Anwarul Hasan1, Michal Fulem2,3 and John M. Shaw2 1 Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, T6G 2G8, Canada 2 Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, T6G 2G6, Canada. 3 Institute of Physics, Academy of Sciences of the Czech Republic, v. v. i., Cukrovarnická 10, CZ-162 53 Prague 6, Czech Republic. Heavy oil and bitumen are characterized by extremely high viscosity that negatively affects their upstream recovery, downstream transportation and refining processes. One of the key factors in facilitating the production and transportation is thus a better understanding of the origination of their high viscosity and the ability to reduce the viscosity to meet pipeline specifications (usually 0.4 Pa.s at operating temperature). The viscosity of heavy oil and bitumen and the structure of asphaltenes are linked to each other. It is known for decades that asphaltene content plays an important role in heavy oil and bitumen rheology with the general trend being that the viscosity increases with increasing asphaltene content. However, the influence of asphaltenes on viscosity has so far been studied on simplified samples where chemically separated (solvent extracted) asphaltenes are dissolved in some standard solvents or in the deasphalted oil (maltenes) to obtain reconstituted samples with different asphaltene concentrations. The question, how closely the nanostructures of such reconstituted samples resemble those arising in the original material remains unanswered in the literature. In this contribution, we report on the rheological properties of Athabasca bitumen and Maya crude oil along with their nanofiltered samples obtained by solvent-free nanofiltration (physical separation) and reconstituted samples prepared by mixing precipitated asphaltenes (chemical separation) and maltenes in different proportions. The rheological properties were studied over wide temperature and frequency ranges. The differences in rheological behaviour between nanofiltered and reconstituted samples, and the origins of these differences are discussed.