The rheological properties of nanoemulsions based on three types of oil phases, namely, Crodamol GTCC, Crodamol PC, and oleic acid, were analyzed and determined. The emulsions were stabilized by Polysorbate 80. Geranic acid was selected as a model active substance. The obtained results confirm that the studied nanoemulsions are pseudoplastic non-Newtonian fluids. The Herschel-Bulkley model accurately describes the rheological properties of the developed systems. The phase inversion point for the Crodamol GTCC/Polysorbate 80/water system was observed at 50 wt% dispersed-phase concentration. The rheological results served as the basis for calculation of a theoretical diffusion coefficient of the active ingredient in the studied nanoemulsions.