This paper reports the significant differences in bed agglomeration behavior during the fast pyrolysis of various mallee biomass components (leaf, wood, and bark) in a fluidized-bud reactor at 500 degrees C. The pyrolysis of mallee leaf and bark led to significant bed agglomeration yields of 12.0 and 13.4%, respectively, while the pyrolysis of the wood component results in little bed agglomeration yield of <0.1%. Ethanol washing of the leaf and bark samples was carried out to prepare solvent-extracted leaf and bark samples (the solid residues after extraction) and the extract samples (obtained after evaporating the solvent from the extracted solvent solutions). Subsequent pyrolysis of the solvent-extracted leaf and bark samples showed drastically reduced bed agglomeration yields of 6.0 and 1.3%, respectively. Direct pyrolysis of the extract samples from leaf and bark resulted in substantial bed agglomeration yields of 24.4 and 34.1%, respectively, suggesting that the extractives within biomass play a critical role in the bed agglomeration during biomass fast pyrolysis. The experimental results indicate that, if the biomass from the whole mallee tree is used as a feedstock for bio-oil production via fluidized-bed fast pyrolysis, then the leaf and bark components are expected to cause bed agglomeration, because of the substantial amount of extractives present in these biomass materials.