We have investigated the effects of glycerol on the formation and rheology of hexagonal phase (H-1) and related O/H-1 gel emulsion in the water/C12EO8/dodecane system at 25 degrees C. It has been found that the aqueous solution Of C12EO8 forms H-1 phase, which could solubilize some amounts of dodecane. Beyond the solubilization limit, oil is separated and a two-phase region or H-1 + O phase appeared. Due to high viscosity of the H-1 phase, allows forming O/H-1 gel emulsion at the H-1 + O region. Rheological measurements (without glycerol) have shown that the rheogram of the H-1 phase does not change drastically with the addition of oil but the system is shifted to longer relaxation time. Simultaneously, the values of the vertical bar eta*vertical bar are found to increase with the addition of oil, which has been described with the neighboring micellar interaction. The rheogram of the O/H-1 gel emulsion shows gel type nature (G' > G '') but the viscosity monotonically decreases with increasing oil content, which could be due to the lower volume fraction of the continuous phase (H-1 phase). Addition of glycerol has brought an order-order transition or the microstructural transition from H-1-lamellar (L-alpha) phase, which is manifested from rheology and SAXS measurements. Viscosity of the O/H-1 gel emulsion also decreases with increasing glycerol content. Digital images show the physical appearance of the gel emulsion changes from turbid to transparent, which is depended on the glycerol concentration (since glycerol matches the refractive index of the H-1 phase and dodecane). Structural parameters of the H-1 phase have been evaluated with the help of Bohlin's model and found that the coordination number of the H-1 phase depends not only the oil and glycerol concentrations but also temperature. (C) 2009 Elsevier Inc. All rights reserved.