The compressed liquid viscosities of 2-methylpentane, 3-methylpentane, and 2,3-dimethylbutane were measured using a vibrating -wire viscometer over the temperature range of (273 to 343) K and at pressures up to 40 MPa. The combined expanded uncertainty of the reported viscosity is about 2% with a confidence level of 0.95 (k = 2). An empirical Andrade-Tait equation was used to correlate the viscosity as a function of temperature and pressure with average absolute percentage deviations of 0.19%, 0.23%, and 0.25%, respectively.