The pyrolytic behavior of four agricultural wastes which are very abundant in Spain (almond shells, wheat straw, grape refuse, and olive stones) has been investigated using a bench scale system. Conventional pyrolysis experiments were performed in a packed bed reactor (58 mm i.d.) at 5, 10, 15, and 30 K min(-1) for a final temperature of 923 K. Temperature profiles, conversion times, product yields (gases, liquids, and char), and gas composition have been analyzed to investigate the influence of the biomass composition and the operating conditions on the process. Large differences were noted in the pyrolysis outputs when the heating rate is increased to 30 K min(-1). In the case of almond shell samples, higher devolatilization rates accompanied by an increase in secondary charring reactions were observed at 30 K min(-1), probably due to the chemical composition of the inorganic fraction present in the almond shells. In addition, when the heating rate is increased to 30 K min(-1), the lignin content does not seem to have a substantial effect on the product distribution. This fact suggests that this heating rate value could be a heating requirement in which the majority of pyrolysis does not occur in the low-temperature region.