The kinetics of the thermal decomposition of Spanish oil shale was studied using isothermal and non-isothermal thermogravimetric analyses (TGA). The isothermal TG data were studied at different particle sizes (0.250 x 10(-3), 0.505 x 10(-3) and 0.925 x 10(-3) m) and three temperature plateaux (703, 688 and 673 K). For the kinetic analysis, the Integral Method was used. The non-isothermal weight-loss data was analysed at different heating rates (5, 10, 15, 20 and 50 K/min) up to 1173 K and for a particle size of 0.250 x 10-3 m. Three methods were applied for the determination of the kinetic parameters: the Direct Arrhenius Plot Method, the integral Method and the Differential Method. From an engineering point of view, the rate of the thermal decomposition of Spanish oil shale can be suitably described by overall first-order kinetics. We also found that transport effect problems affected the observed rate when the heating rates were higher than 10 K/min; additionally, no mass and heat transfer resistance was observed for the different particle sizes studied. The results obtained from the isothermal method give an apparent activation energy of 150 kJ/mol and a frequency factor of 2.11 x 10(8) s(-1), while for the non-isothermal method these results were: E = 167 kJ/mol and A = 2.16 x 10(9) s(-1). The pyrolysis rates of Spanish shale are compared with those of Anvil Points, Clear Creek and Moroccan shale. (C) 2001 Elsevier Science Ltd. All rights reserved.