The aim of this work is to present and discuss a detailed kinetic model that describes the devolatilization process of solid fuels under pyrolysis conditions. The major reason for this interest in better understanding pyrolysis and combustion of coal, biomasses and solid fuels lies in the increasing concern for the environmental impact of large scale combustion processes. The common chemical and structural aspects of the different fuels are singled out and used as the starting point to define this mathematical model. The formation of light gases and liquid tars is the first step in the pyrolysis process. Particular attention is also devoted to the generality and flexibility of numerical and mathematical methods. Two major critical points are present inside this model: the first is related to the definition of the initial structure of the fuel and the second is constituted by the set of reference kinetic parameters of the different reactions. Several comparisons with experimental data are analysed and the molecular weight distributions of the tar from different coals evolved at different temperatures are also discussed. (c) 2004 Elsevier Ltd. All rights reserved.