We have investigated the effects of glycerol on the formation and theological behavior of cubic phase (I-1) and related O/I-1, gel emulsion in a water/C12EO8/dodecane system at 25 degrees C. The phase behavior of the wateF/C12EO8/dodecane system was studied by optical observation and structures of different liquid crystalline phases were identified by small-angle X-ray scattering (SAXS) techniques. Addition of dodecane (2 wt%) to aqueous solutions Of C12EO8 in a concentrated region (40 wt%) leads to the formation of the I-1 phase (which was absent without the addition of oil). The I-1 phase solubilized some amount of oil and at higher oil concentrations the I-1 + O phase was formed, allowing the Preparation of O/I-1 gel emulsion. Rheological measurements have shown that the complex viscosity, vertical bar eta*vertical bar, of the I-1 phase is tremendously high (similar to 10(7) Pas) and it increases with increasing oil concentration, attains a maximum value near the phase boundary, and then decreases drastically in the I-1 + O region. The increasing vertical bar eta*vertical bar or decreasing tan delta(G ''/G') can be ascribed with the interactions among the neighboring micelles. The decreasing trend of the vertical bar eta*vertical bar in the I-1 + O region is simply due to the low volume fraction of the I-1 phase. It has been shown that glycerol decreases the viscosity of the I-1 phase and related gel emulsion, which is due to the I-1-hexagonal phase (HI) microstructural transition. Digital images show the physical appearance of the emulsion, which depends on the glycerol concentration changes from translucent to transparent. (C) 2008 Elsevier Inc. All rights reserved.