Flexibility in the supply of biomass to the energy conversion facility, as a function of the seasonal availability, is considered as one of the keys to guarantee their continuous operation and the yield of the investments. The kinetics of devolatilisation of the two most typical biomass wastes in the middle-south regions of Spain, wastes from pruning of pine and olive trees, were studied using thermogravimetric analysis, in order to evaluate their use in combination as an energy feedstock throughout the year. A kinetic devolatilisation model was fitted to the experimental results and the kinetic parameters were obtained. Although slightly different behaviour was found between different categories of the same sample (large branches, small branches and needles or leaves), the differences between pine and olive wastes were not significant, which indicates that they can be combined for use in combustion or gasification systems. (c) 2006 Elsevier Ltd. All rights reserved.