non-newtonian fluids, such as polymer solutions, have been used by the oil industry for many years as fracturing agents and drilling mud. these solutions, which normally include thickened water and jelled fluids, are injected into the formation to enhanced oil recovery by improving sweep efficiency. it is worth noting that some heavy oils behave non-newtonianly. non-newtonian fluids do not have direct proportionality between applied shear stress and shear rate and viscosity varies with shear rate depending on whether the fluid is either pseudoplastic or dilatant. viscosity decreases as shear rate increases for the former whilst the reverse takes place for dilatants. mathematical models of conventional fluids thus fail when applied to non-newtonian fluids. the pressure derivative curve is introduced in this descriptive work for a dilatant fluid and its pattern was observed. tiab's direct synthesis (tds) methodology was used as a tool for interpreting pressure transient data to estimate effective permeability, skin factors and non-newtonian bank radius. the methodology was successfully verified by its application to synthetic examples. also, comparing it to pseudoplastic behavior, it was found that the radial flow regime in the newtonian zone of dilatant fluids took longer to form regarding both the flow behavior index and consistency factor.