In this paper, optimization techn ques were applied in the characterization of the thermodynamic behavior of Supercritical Water Gasification (SCWG) of different biomass source , like as ethanol, glycerol, lignin, microalgal biomass (Nannochloropsis sp.) and sugarcane bagasse. For this, the Gibbs energy minimization (at constant pressure and temperature) and entropy maximization (at constant pressure and enthalpy) methods were applied in combination with the Virial equation of state, using non-linearprograming. The problems were solved in the software GAMS using the CONOPT solver. The effect of modifications in biomass source was analyzed on H2 production and on the thermal behavior of the SCWG systems. High H2 production was observed for all substrates and the highest productions were observed for the SCWG of ethanol at isothermic conditions. The entropy maximization has shown that, with the exception of the SCWG of ethanol, all other SCWG presented autothermal behavior for initial temperatures below 1100 K. However, at adiabatic conditions the highest productions of H2 were observed for the SCWG of glycerol, mainly due to high exothermic behavior of this system. With the results, it is possible to conclude that all biomass sources tested presented potential for application in H2 production.