This contribution discusses the analytical challenges arising by the measurement of complex phase equilibria over a large temperature range for the system non-ionic surfactant + water + olefine. Using these substances three- und two-phase states will occur. The challenge is on the one hand the strong limited solubility of oil in water and of water in oil, respectively. Therefore, standard analytical equipment is close to its detection limit. The used analytical tools are high-pressure chromatography and two different approaches for the Karl-Fischer water titration.