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In this study, liquid–liquid equilibrium measurements were performed for different ternary, water (or brine)/decane or dodecane/mono-propylene glycol ether (C 3 P 1 ) or di-propylene glycol ether (C 3 P 2 ) systems in order to build the so-called fish phase diagrams (temperature as a function of surfactant for a given polar-apolar solvent mixture) and to compare them to the well-known water (or brine)/decane or dodecane/ethylene glycol mono-butyl ether (C 4 E 1 ) phase diagrams. The study is motivated by the lower toxicity of the C x P y compared to the corresponding C x E y . Toxicity is of particular importance for any use of such molecules in the environment. Like in the presence of C 4 E 1 , the formation of Winsor type I → III → II phase transitions with increasing temperature was observed for the C x P y systems. The LCST (Lower Critical Solution Temperature) and UCST (Upper Critical Solution Temperature) of the newly studied systems were determined. The values of the γ 0 parameter (in mole fraction), the minimum value of surfactant needed to form Winsor III, increased in comparison to the C 4 E 1 systems. The value of γ ˜ (in mole fraction), minimum value of surfactant needed to reach Winsor IV from Winsor III, was comparable using C 4 E 1 and C 3 P 1 , and lower in the presence of C 3 P 2 . The substitution of decane by dodecane led to a stronger water affinity of C 4 E 1 and C 3 P 2 as greater values of the LCST and UCST have been observed in the presence of dodecane. By contrast, a lower hydration of C 4 E 1 and C 3 P 1 was found when increasing the NaCl content in brine. It can be concluded that less toxic C 3 P 1 and C 3 P 2 can be envisaged as a substitute of the contested C 4 E 1 to formulate microemulsions and particularly Winsor III systems. [ABSTRACT FROM AUTHOR]