The viscosity of heavy crude oils strongly affects their producibility and recovery from oil reservoirs. Thus, the viscosity of heavy crude oils with dissolved gases at different shear rates is valuable knowledge for heavy crude oil exploitation. However, most publications only present viscosity measurements at one specific shear rate, and only a few papers in the literature have reported the rheological measurements over a range of shear rates. In this study, viscosity measurements of CO2-saturated heavy crude oils were performed as a function of the shear rate, at a temperature of 25 degrees C and pressures up to 220 bar. The experimental apparatus is a unique circulation system, which is able to measure the viscosity of CO2-saturated mixtures. A novel high-pressure rheometer with a flow-through Couette geometry was developed to measure the viscosity at a range of shear rates. The experimental results show that the addition of CO2 to heavy crude oil at the given temperature and pressures reduces the viscosity significantly, but the pressure dependence of the mixture viscosity changes at the phase transition of the CO2-rich phase. A modified Arrhenius equation, accounting for the effect of CO2 composition on viscosity, is applied to correlate the viscosity data.