Viscosity measurements of Fe73S27 (wt%) liquid at pressures between 2.0 and 5.0 GPa and at temperatures in the range 1100--1300 ¿C have been made using Stokes' method of rising spheres in conjunction with a newly developed electro-detection technique. The viscosities range from 43.6¿7.0 Pa-s at 3.9 GPa and 1100 ¿C to 1.6¿0.5 Pa-s at 3.0 GPa and 1300 ¿C. These high P viscosity values are three orders of magnitude higher than the 1 atm values and are tentatively attributed to the effects of S on the size of viscous flow units. From the T and P dependences of viscosity, activation energy and volume, respectively, have been determined. Activation energy decreases with increasing P, from 405¿77 kJ/mol at 2.0 GPa to 240¿72 kJ/mol at 5.0 GPa, and activation volume increases with increasing T, from 1.51¿0.01 cm3/mol at 1100 ¿C to 3.61¿0.19 cm3/mol at 1300 ¿C. ¿ American Geophysical Union 1996