In olive-oil producing countries, large amounts of waste material are generated as by-product for which there is no ready use and in some cases may have a negative because of the cost of disposal. Most of these countries depend on fossil fuels for their energy uses, and olive-oil residue can be used to supplement such energy sources using thermochemical conversion processes. However, efficient operation of thermochemical conversion systems requires a thorough understanding of the influence of the composition and thermal properties of these by-products on their behaviour during the conversion process. In this study, the thermal behaviour of two olive-oil residue samples (non-leached and water-leached olive-oil residue) was examined at three heating rates (10, 20 and 50 degrees C min(-1)) in air atmosphere using the technique of thermogravimetric analyses. The thermal degradation rate in active and passive zones, the initial degradation temperature, and the residual weight at 700 degrees C were determined. Increasing the heating rate increased the thermal degradation rate, the residual weight at 700 degrees C, and the initial degradation temperature. The thermal degradation rate and the initial degradation temperature increase with the cellulose content of the olive-oil residue. Also, higher ash content in the olive residue resulted in higher residual weight at 700 degrees C. (c) 2005 Elsevier B.V. All rights reserved.