The viscosities of the mixtures 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM][PF6]) + CO2 and 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF6]) + CO2 were measured with a rolling ball viscometer. The CO2 mole fraction for one mixture ranged up to 0.434 and the other up to 0.447. The viscosities were measured at 293.15-353.15 K and 10-20.0 MPa. The experimental uncertainty in viscosity was estimated to be within +/- 3.0%. The experimental data were compared with McAllister's three-body model, which correlated with the experimental data within average absolute deviations of 5.9%. (C) 2011 Elsevier B.V. All rights reserved.