The paper compares the microstructural properties and the intrinsic reactivity of pine seed shells, olive husk and wood chips upon pyrolysis, combustion and gasification (with CO2 and H2O). Such biomasses, all of interest in energy production, are quite different from one another in terms of O/C and H/C content, of porosimetric structure and of ash content. An extensive campaign of isothermal and non-isothermal thermogravimetric experiments allowed to assess the reactivity of the fuels and to obtain kinetic expressions for the main reactive processes (pyrolysis, char combustion and char gasification). Olive husk turned out to be the most reactive material, followed by wood chips and pine seed shells. Differences of reactivity are particularly pronounced in the case of char combustion. The high reactivity of olive husk has been related to its high content of mineral inclusions, compared with the other biomasses, coupled with a relatively accessible porous texture. The porous structure of the biomass chars turned out to determine also the changes in reactivity along conversion. (C) 2006 Elsevier B.V. All rights reserved.