Shear viscosity coefficients, volumetric properties, and equilibrium-phase compositions for CO2/West Texas oil mixtures are presented. Effects of solution gas, nitrogen in the CO2 stream, and viscosity dependence on phase density and CO2 concentration also are examined. The work shows that measured CO2-rich phase viscosities increased as solution gas in the oil increased. Nitrogen in the CO2 stream results in lower CO2-rich phase viscosities and densities compared with those from an identical sun with pure CO2 solvent. CO2/crude-oil viscosity measurements reveal viscosity and density behavior patterns that are unique to these systems. Undersaturated CO2/crude-oil mixtures show an abnormal viscosity dependence on density. The viscosities show a monotonic decrease, while the densities increase with continued dilution of the oil with CO2. The equilibrium vapor (dense fluid) and liquid phases, however, exhibit normal viscosity/density behavior. Data are compared with a popular reservoir-fluid-viscosity correlation commonly used to estimate CO2/crude-oil viscosities in reservoir simulation studies. We show that the correlation cannot predict CO2/crude-oil-system viscosities accurately.