The effect of triglyceride molecular weight on the formation and rheology of cubic (O/I-1) and hexagonal (O/H-1) phase based gel emulsions has been studied in water/C12EO8 systems. It was found that the addition of TDG (1,2,3-tridecanoyl glycerol) in the micellar solution leads to the formation of the I-1 phase, which can solubilize some added oil. From SAXS data, it is revealed that the interlayer spacing (d) and the length of hydrophobic part (r(1)) increase with increasing TDG concentration in the I-1 phase, whereas the effective cross-sectional area (a(s)) decreases. After the oil solubilization limit, the d value remains nearly constant, indicating the I-1+O phase appears. The high viscosity of the I-1 phase facilitates the formation of the O/I-1, gel emulsion. It has been observed that the formation and stability of the O/I-1, and O/H-1 gel emulsion is highly dependent on the molecular weight of triglycerides, namely, the high molecular weight triglycerides show better performance (formation and stability) compared to the low molecular weight triglycerides. The theological behavior of the I-1 phase was found to change from viscoelastic to elastic nature with TDG content. The values of the complex viscosity, vertical bar eta*vertical bar show different trends at different fixed frequencies within the I-1 phase, whereas it decrease monotonically in the O/I-1, gel emulsions. The increasing values of the vertical bar eta*vertical bar (at lower frequency) could be due to the neighboring micellar interaction and decreasing values of the vertical bar eta*vertical bar in the O/I-1, gel emulsion could relate to the volume fraction of the I-1 phase in the system. It is also figured out that the rheological parameters (elastic modulus, viscous modulus, and vertical bar eta*vertical bar)of the O/I-1, the gel emulsion do not depend on the oil nature, whereas the O/H-1 gel emulsion shows oil nature dependency. (C) 2009 Elsevier Inc. All rights reserved.