The rheology of slurries prepared from artificial mixtures of bitumen with fine quartz of varying bitumen content, as well as slurries of actual oil sand ores, was investigated under different physicochemical conditions (pH and temperature). All rheological measurements were conducted using a Haake Rotovisco VT550 rotational viscometer, connected to a fixture specifically designed to measure the rheological properties of settling suspensions. It was found that when the bitumen content in slurries prepared from quartz-bitumen mixtures was low (0.7 vol. %), the pH of the slurries was the most important parameter that controlled the rheology of these slurries. At higher bitumen contents (8 vol. %), it was a combination of high temperature and high pH that gave the lowest apparent viscosities and yield stresses of the model mixtures. These model observations correlated well with the rheology data obtained for slurries of actual oil sand ores. The overall results were discussed in terms of aggregation-dispersion phenomena between bitumen and mineral particles. (C) 2012 The Society of Rheology. [http://dx.doi.org/10.1122/1.4708340]