This manuscript is the first report that discusses the phase behavior of a ternary system composed of water, nonionic surfactant C12E8, and 1-dodecene. The phase behavior (Kahlweit fish and tie lines at different temperatures) of this ternary system was investigated based on the phase behavior of the water + C12E8, water + 1-dodecene and C12E8 + 1-dodecene binary subsystems. Novel experimental liquid-liquid equilibrium data are presented for the three corresponding subsystems. The data obtained for the water + C12E8 system was compared with data from the literature. The phase prism of the ternary system was measured over a wide temperature range using several analytical methods (Karl Fischer titration and HPLC). The general phase behavior is very similar to the well-known phase behavior of water + nonionic surfactant + alkane systems. Classical Winsor-type phase behavior was established within the ternary system depending on the temperature. At 354.15 K, a middle-phase microemulsion, which contained 1-dodecene and water mass fractions of approximately 0.2 and 0.6, was found. This phase behavior can be exploited for chemical reactions, such as the hydroformylation of 1-dodecene to yield 1-tridecanal through the use of the water-soluble and very expensive Rh catalyst at temperatures at which the middle-phase microemulsion exists. (C) 2012 Elsevier Ltd. All rights reserved.