The viscosities of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) + CO2 mixtures were measured with a rolling ball viscometer. The experimental temperatures were from (293.15 to 353.15) K, and pressures were up to 20.0 MPa. The CO2 mole fractions of the mixtures were in the range up to 0.440. The McAllister four-body model has been used to correlate the viscosity data.