A wide characterization of the phase equilibrium involved in aqueous biphasic micellar systems (ABMSs) formed by 10,000 or 35,000 g mol(-1) polyethylene glycol (PEG) + t-octylphenoxypolyethoxyethanol (Triton X-100) + water was evaluated at 283.15, 298.15, and 313.15 K, respectively. The influences of temperature, polymer molar mass, and mixture compositions on the phase diagrams obtained were evaluated. The analysis of the phase diagrams obtained experimentally showed that the increase of temperature favors, significantly, the phase separation process. The increase in the polymer molecular weight from 10,000 to 35,000 g mol(-1) has an even more pronounced effect than that of temperature in inducing phase separation. The experimental liquid-liquid equilibrium (LLE) data were then theoretically correlated using the extended Flory-Huggins lattice model for ternary mixtures. The interaction parameters of the component's pairs PEG-Triton X-100 (lambda(12)), PEG-water (lambda(13)), and Triton X-100-water (lambda(23)) in the ABMSs were estimated at different temperatures and in two different surfactant configurations (single molecule and micellar aggregates). Although it was not possible to correlate the parameters of interaction with the physical reality of ABMSs, the Flory-Huggins model allowed to recover the LLE data within the experimental error range. The experimental data of the binodal curves for the different ABMSs were also adjusted through the Othmer-Tobias, Bancroft, and Setschenow empirical equations.