The paper reports on gasification of almond shells with water at high pressure (above critical value) and temperature. The experimental set up was a semi-continuous reactor, an innovative configuration allowing to continuously remove the gas product from the reaction vessel. The adoption of pressure conditions well above water critical value (30 MPa) and relatively low temperature (300 C) confirmed suitable reaction pathways for biomass conversion with high efficiency leading to a liquid phase rich of some interesting compounds (HMF, furfural). In order to increase the process performances, sodium hydroxide was added as promoter of the gasification reactions. According to an already proposed reaction scheme, results confirmed a positive impact of the additional compound to the liquid yield and quality, while the gaseous phase was enriched in carbon dioxide. © 2013 Elsevier Ltd. All rights reserved.