In low-energy emulsification processes, phase inversion occurs when the phases of a dispersion exchange, because of changes in the medium's properties. This paper reports experiments to determine the phase inversion temperature (PIT) of orange oil=water emulsions stabilized by nonionic surfactants. Two techniques were employed: rheology, which is already commonly used to obtain the PIT, and microcalorimetry, which has been proposed as a new technique. Continuous monitoring of the emulsions' viscosity permitted identifying different phenomena that occur while the temperature varies. For all the dispersions prepared, the rheological curves obtained showed two peaks, one attributed to the phase separation process and the other to the phase inversion phenomenon. The microcalorimetry technique showed two endothermic transitions as the dispersion's temperature increased. The initial temperatures were comparable to those obtained by rheology. The influence of the surfactant concentration and the hydrophilic-lipophilic balance (HLB) of the mixture of surfactants and the reduction in volume of the phases at the phase inversion temperature were also evaluated. In general, both methods used to evaluate the phase inversion of the orange oil=water systems (rheology and microcalorimetry) presented concordant results, both for the phase separation process and the phase inversion temperature.