Capillary viscometer data are reported for 0, 15, and 30 vol. % glass fiber suspensions in 100, 600, and 1000 P silicone oils. All other suspension parameters, including fiber length distribution, were constant. Wall effects were not significant. The viscosity data at each concentration were fit by a dimensionless plot of the formF(fNRe,NEl)=0whenfis the friction factor for tube flow andNReandNElare the Reynolds and Ellis numbers of the system. Suspension viscosity increased with fiber concentration, but the magnitude of the increase was highly shear rate dependent. The dependence of viscosity on fiber concentration and shear rate is compared with literature predictions.