Pyrolysis may be a first step in biomass to biofuels conversion processes. The present study investigated the influence of pressure on the thermal effects associated to biomass pyrolysis. Four energy crops were selected for experimental characterization: corn stalks, poplar, switchgrass Alamo and switchgrass Trailblazer. The heat demand of the pyrolysis process was measured by differential scanning calorimetry at pressures ranging from 0.1 to 4 MPa, using a specifically developed experimental configuration. An increase of the operating pressure resulted in a lower heat demand and in an increase in the final char yield. The results obtained suggest the presence of a competitive mechanism between the endothermic reactions of the primary decomposition process, leading to the formation of volatiles, and the exothermic vapor-solid interactions, leading to secondary char formation. (C) 2014 Elsevier Ltd. All rights reserved.