As the demand for energy grows, sustainable energy sources like plant biomass become increasingly important. Plant biomass consists of three main components: cellulose, hemicellulose and lignin. Phenol is a model compound for the phenolic structures comprising the lignin in biomass. Also the macromolecular chemical structure of biomass contains many phenolic monomers. In this study, gasification of phenol as a model substance for plant biomass waste was carried out in supercritical water at a temperature range 400 to 600 degrees C and for the pressures 20.0, 27.5, 35.0 and 42.5 MPa. Experiments were performed in the absence and presence of alkali catalyst potassium carbonate (K2CO3) for a reaction time of 1 h. Both the gas and liquid phases were analyzed by using chromatographic techniques, which identified and quantified the reaction intermediates and products, including H-2, CH4, CO2, CO and C-2-C-4 hydrocarbons, in the gas phase and different compounds (carboxylic acids, furfurals, aldehydes and ketones) in the liquid phase. Higher temperatures and using catalyst K2CO3 promoted gasification and resulted in a product gas rich in CH4 and H-2. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.