The high-pressure rheology of a soap-thickened grease and the base oil has been characterized using a falling-body viscometer, high-pressure Couette viscometer, and a high-pressure penetrometer. At shear stress from 0.1 to 1 MPa, the response of the grease was approximately linear with rate of shear with a viscosity about twice that of the base oil. Apparent yield stress behavior is observed at lower shear stress. A new modified Bingham model is offered to describe the experimental observations. These results are relevant for simulations of elastohydrodynamic lubrication and journal bearings operating at elevated ambient pressure.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993