When the emulsion inversion from an abnormal oil-in-water (O/W) system to a normal water-in-oil (W/O) morphology is produced by continuous stirring, the fraction of dispersed phase at which the inversion is triggered (which is known as the critical dispersed phase fraction) and the inversion mechanism are affected by a change in viscosity. As the viscosity of any of the phases increases, the critical dispersed phase fraction decreases. When the oil phase has a similar or higher viscosity than the water phase, inversion occurs via the formation of a multiple emulsion w/O/W, in which the "W" external phase is continuously included as "w" droplets in the dispersed "O" phase drops. Hence, the apparent volume of the dispersed phase increases until a critical value is reached and the inversion is triggered. On the other hand, if the water phase is much more viscous than the oil phase, the experimental evidence suggests that the inversion occurs through the formation of a pseudo-fibrous structure, in which the connectivity of the internal phase is produced by drop elongation.