The supercritical water gasification process is an alternative to both conventional gasification as well
as the anaerobic digestion processes for conversion of wet biomass. This process does not require drying
and the process takes place at much shorter residence times; a few minutes at most [3,5]. Supercritical
water gasification is therefore considered to be a promising technology for the efficient conversion of
wet biomass into a product gas that after upgrading can be used as substitute natural gas. The earliest
research goes back as far as the 1 970s [6] and since then, supercritical water has been the subject of
many research works regarding the thermochemical conversion of wet biomass [7–9]. This article
reviews the state of the art in supercritical water gasification technology, starting from the thermophysical
properties of water and the chemistry of reactions to the process challenges of such a supercritical water
gasification of a biomass processing unit.