A kinetic model to describe the catalytic pyrolysis of tars is proposed and validated through the experimental pyrolysis of three tars of different characteristics and origin; calcined limestone (11 m(2)/g) was used as catalyst. Experiments were carried out in a catalytic fixed bed reactor. The model assumes that tars are composed of two pseudo-components, described as heavy and light tars, which can be experimentally determined by a split temperature. Tar pyrolysis is described by two simultaneous chemical reactions; catalyst deactivation due to carbon deposition is also considered. Expressions for product concentrations as functions of residence time, selectivity and deactivation were obtained and the kinetic parameters evaluated. (C) 2001 Elsevier Science B.V. All rights reserved.