This work examines the variability in fluid leakoff rates measured under static and dynamic conditions. Laboratory-generated data are compared to field-measured data, and the conditions under which static and dynamic data should be used for fracture design are examined.Control of fluid leakoff in both the low-permeability matrix and highly permeable natural fractures is examined on formation cores under a variety of conditions. The control mechanism offered by various fluid-loss additives is evaluated by examining the fluid-matrix and fluid-filtercake interactions.