Rheology of Microfibrillated Cellulose (MFC) suspensions is useful for designing equipment to transport, mix, or process them. Pressure-driven flow behavior is particularly important for MFC suspensions if they are to be pumped, extruded or coated. Herein, we report use of slot and pipe geometries for determination of MFC suspension rheology and compare the results to boundary-driven flows. MFC flow behavior in a slot with varying gaps was studied at mass concentrations of 1, 2, and 3% and up to shear rates of 100 000 s-1. The suspensions exhibited yield stress and were highly shear thinning (pseudo-plastic) with apparent power law indices of 0.22 – 0.43. The shear thinning behavior can be explained by a microstructural picture in which a non-yielding center plug is surrounded by a yielded layer and a fiber-depleted water rich boundary layer.