The present paper addresses thermal annealing of coal under the combined effects of temperature and pressure. Coal particles were pyrolysed in a pressurized heated grid reactor with heating rate of 5000 degrees C/s up to 1600 degrees C. The pressure during heat treatment was set to values in the range 1-12 bar. After heat treatment char samples were collected and subjected to: 1. Isothermal and non isothermal thermogravimetric analysis, in order to measure their reactivity towards oxygen, carbon dioxide and mixtures of oxygen-carbon dioxide. 2. XRD and porosimetric analysis in order to investigate their structure. 3. Laser light scattering particle analysis in order to assess the extent of fragmentation experienced during heat treatment. Results show that upon heat treatment coal particles undergo severe thermal annealing and extensive fragmentation. For a given temperature of heat treatment, the effect of pressure of char preparation turns out to be non monotonous: at 1500 degrees C both char porosity and reactivity pass through a minimum at pressure in the order of 2-5 bar. The probability of fragmentation and the degree of graphitization follow a specular trend, with a maximum at pressures of 2-5 bar. (C) 2013 Elsevier Ltd. All rights reserved.