Hydrogen production by supercritical water gasification (SCWG) of biomass is a unique process of producing energy without drying of the biomass. Especially liquid by-product streams offer via SCWG the possibility of energetic utilization in comparison to waste disposal. In this paper the parameters temperature, residence time, TOC-concentration of the feed and potassium carbonate as catalyst for the hydrothermal gasification of pyroligneous acid are studied. Pyroligneous acid is a liquid by-product of charcoal production mainly composed of acetic and formic acid. Results measured with different lab-scale reactors and a pilot plant with a maximum throughput of 100 kg/h are presented. The experiments show an increase of gasification efficiency at high temperatures, low TOC-concentration of the feed, moderate residence times and the addition of potassium carbonate. (C) 2011 Elsevier Ltd. All rights reserved.