A laboratory-scale countercurrent fixed-bed gasification plant has been designed and constructed to produce data for process modeling and to compare the gasification characteristics of several biomasses (beechwood, nutshells, olive husks, and grape residues). The composition of producer gas and spatial temperature profiles have been measured for biomass gasification at different air flow rates. The gas-heating value always attains a maximum as a function of this operating variable, associated with a decrease of the air-to-fuel ratio. Optimal gasification conditions of wood and agricultural residues give rise to comparable gas-heating values, comprised in the range 5-5.5 MJ/Nm(3) with 28-30% CO, 5-7% CO2, 6-8% Hz, 1-2% CH4, and small amounts of C-2- hydrocarbons (apart from nitrogen). However, gasification of agricultural residues is more difficult because of bed transport, partial ash sintering, nonuniform flow distribution, and the presence of a muddy phase in the effluents, so that proper pretreatments are needed for large-scale applications.