Torrefaction is a way to treat biomass before transportation or thermochemical conversion. It can be used to increase the energy content of wood or to facilitate grinding. The purpose of this paper was to quantify the impact of such a treatment on the behaviour of wood during gasification by steam at high temperature to produce syngas. The aspects of both gas yields and reaction kinetics were considered. Beechwood was submitted both to light torrefaction and severe torrefaction, using a specially designed crossed fixed bed reactor. The initial wood and the torrefied woods were first characterised, then gasified in a new laboratory high-temperature entrained flow reactor (HT-EFR) at 1400 degrees C for 2 s in an atmosphere containing 20 vol% steam in N(2). The syngas produced was then analysed. The experiments were modelled using a thermo-dynamical equilibrium approach. It was confirmed that torrefaction decreased the O/C ratio. The quantity of syngas produced increased with the severity of the torrefaction. The equilibrium approach describes the results satisfactorily. Gasification experiments carried out at a lower temperature - 1200 degrees C - indicated that the chars from torrefied woods are less reactive towards steam than the char from wood. (C) 2009 Elsevier Ltd. All rights reserved.