Abstract The solid medium deformation experiments on polycrystalline olivine at pressures of 500–1500 MPa show steadily increasing creep strength with decreasing water content. Thus water content can significantly influence the strength of olivine. Room pressure experiments on olivine single crystals have been conducted under conditions of low p H 2 O and therefore should be compared with solid medium experiments on dried samples deformed under anhydrous conditions. The single crystals flow more rapidly by 2–3 decades in strain rate for a given stress. Three hypotheses regarding the origin of this strength discrepancy are: 1. (1) solid medium sample strengths are higher due to the finite strength of the confining medium; 2. (2) temperature gradients in the solid medium samples render them stronger; 3. (3) the application of high confining pressure has significantly increased strength. These hypotheses have been analyzed and none of them appears to alter strain rates by more than a decade. Another hypothesis, that dislocations are pinned by iron oxide precipitates in the “dry” solid medium experiments, also does not appear likely. Unless some unknown effect in the solid medium apparatus results in anomalously high strength for olivine, the discrepancy must be attributed to fundamentally different behavior of the single crystal and the aggregate.