A residue obtained after the distillation of agricultural alcohol called beet residues is gasified in supercritical water to form a mixture of fuel gas. A parametric study and thermodynamic calculations are first proposed in batch reactor. The results show a significant effect of temperature on the overall mass yields. Gasification efficiencies range from 0.60 to 0.90 g g−1 when temperature increases from 450 to 600 °C. The gas low heating value increases under these conditions from 7.4 to 13.2 MJ kg−1 of initial dry feedstock. After that, a continuous system designed for hydrothermal oxidation processes has been used. For supercritical water gasification, the reduction of total organic carbon in the liquid effluent output presents a little variation, between 59 and 69%, when the operating conditions are changed. To increase the reaction temperature, supercritical water partial oxidation has been conducted. The highest carbon gasification yield is obtained for the highest equivalent molar ratio, indicating a great interest of partial oxidation. Moreover, the results indicate that this process configuration accepts biomass flow variations without influencing the global efficiency.