Liquid and vapor viscosities are reported for the binary refrigerant mixtures (R125 + R152a), (R125 + R1234ze(E)), (R143a + R1234ze(E)), (R143a + R1234yf), and (R1234ze(E) + R1234yf). The measurements were made with a vibrating wire viscometer and span temperatures from (252 to 403) K and pressures from (0.9 to 4.0) MPa. The performance of the vibrating-wire apparatus was validated by measuring the viscosity of pure R152a in both the vapor and liquid regions. These measurements and previously published data were used to tune binary interaction parameters in the extended corresponding states equation model for viscosity implemented in the NIST software REFPROP 9.1. After tuning, deviations between the model and reported viscosities were reduced from between (-4 and 8)% to within ±2%.