This paper presents a set of calorimetric measurements with the aim of better understanding the calorific nature of hydrothermal carbonization. Presented values so far show an inadequately high scatter to do so, preventing a well funded assessment of the energetic feasibility of this process. The heat released during hydrothermal carbonization at 240 degrees C measured with the applied differential calorimetry setup is -1.06 MJ/kg(glucose,daf) with a standard deviation of 14%, -1.07 MJ/kg(cellulose,daf) With a standard deviation of 9%, and -0.76 MJ/kg(wood,daf) with a standard deviation of 32%. These results are in good agreement with the theoretically derived maximum heat release. Despite the comparably high experimental standard deviation of these results, their accuracy is considerably higher than previously published results. (C) 2011 Elsevier Ltd. All rights reserved.