Hydrothermal gasification of biomass in supercritical water is one of the rare pathways that potentially allows for a complete conversion of wet waste biomass into Synthetic Natural Gas (SNG). This paper summarises an extensive process design study and discusses some key aspects of the process integration and, in particular, the influence of the feedstock on the optimal process design and its performances. It thereby demonstrates that the process design and performance is not only influenced by available technology, catalyst deactivation issues and scale, but also the characteristics of the processed substrate.