The aqueous-phase behavior of C12E2 was examined using the diffusive interfacial transport-near infrared method (DIT-NIR), a new isothermal swelling method fdr assembling accurate and precise phase diagrams. The system exhibits a large number of liquid-crystal phases over a remarkably small temperature and composition window including a sponge phase, two bicontinuous cubic phases, and a lamellar phase. The phase behavior of the system is similar to Class II polar lipids, such as monoglycerides, excluding the liquid-liquid miscibility gap and the sponge phase associated with ethoxylated surfactants. The data collected by the DIT-NIR method provide a marked improvement to the currently accepted phase diagram. Finally, temperature steps can create temperature-induced cubic-phase-containing emulsions in which pyramidal-shaped L1 droplets are dispersed within the V-2((1)) bicontinuous cubic-phase continuum, reflecting the epitaxy of the cubic-phase lattice.