The applications of product gas are found in the production of power and/or heat. The utilisation of biomass-based product gas is not (yet) completely established and for the more advanced applications the technologies are still in development. Resultantly, also the technical gas specifications have not yet been defined. More important for heat and power production, however, are the applicable emission regulations that in most cases will results in more stringent gas specifications than required for technical reasons. Typical limits standards apply for emission of dust, CO and/or CH4 (indicators for incomplete conversion), NOx (from fuel- NH3 and thermal NOx), SO2 (from fuel S), volatile metals, and PAHs.