A parametric study of the gasification of four feedstocks (corn stover, switchgrass, wheat straw, and wood) has been performed on an experimental, pilot-scale (0.5 ton/day) gasification facility. A comparison was made of the performance of the gasifier as a function of feedstock, in terms of the syngas production and composition. In these experiments, pelletized feedstock was used, so that the shapes and sizes of the materials did not influence the results. A total of 22 statistically designed experimental conditions were examined for each feedstock, including the effects of varying the temperature of the fluidized bed, the temperature of the secondary thermal cracker, and the steam-to-biomass ratio. For each experimental condition, the permanent-gas composition was measured continuously by gas chromatography (GC). Tars were measured continuously using a molecular-beam mass spectrometer (MBMS). Sulfur analysis by GC was also conducted for three of the feedstocks Studied. The results from this study show that there were significant differences between the feedstocks studied in terms of light gases formed, but less apparent variation in tar formation. In general, the variations in products were smaller at higher temperatures. A preliminary analysis of gasifier efficiency was performed using an Aspen Plus process model for selected gasification conditions. Finally, a comparison was made between the results of this work and other similar biomass gasification studies.