The forces generated by flow between eccentric rotating disks (ERD) are examined experimentally. ERD experiments are presented for several Newtonian and viscoelastic fluids with viscosities ranging from 30 to 240 000 poise. The effects of disk separation, radius, misalignment, and eccentricity are studied. ERD data is compared to the dynamic shear moduli, G′ and G″, defined by small amplitude deformation in oscillatory shear flow. Results confirm theory that the two measurable shear forces generated in the ERD do measure G′ and G″. No significant boundary or inertial effects were noted, but in some cases instrument compliance can be significant. Normal stress measurements in the ERD are also reported.