Differential scanning calorimetry (DSC) and viscoelastic measurements were carried out for oil gels formed by styrene-butadiene-styrene triblock copolymer (SBS) and naphten oil or 1-octadecene to investigate the mechanism of their gelation. There were three endothermic peaks in the DSC curves assigned as the glass transition of the butadiene units, that of the styrene units, and the dissolution enthalpy of the styrene units and solvent oils. The G' of the SBS gels showed a specific depression near the glass transition temperature of the styrene units, determined by DSC. The modulus curve had also a shoulder at the gel melting temperature determined by the tilting test tube method. The structure and gelation mechanism of SBS gel were discussed on the results of the measurements.