The preparation of a biomass conversion technology and cost data bank for the Biomass Energy Systems Branch (BES) of DOE/Solar is described. Technical and economic analyses of a number of BES technology options are currently underway. A total of 22 biomass conversion technology options (14 thermochemical and 8 biochemical) have been selected for inclusion in the data bank. These options cover the production of electric power, steam, gases, liquids, and solid fuels from biomass. The majority of the options are believed to be available now or in the near term. A consistent methodology for construction of the data bank has been developed. For each option, the most up-to-date process/product data are gathered and analyzed. A base case is established to generate estimates for plant investments required, operating cost, and product cost. The estimates are then examined systematically to identify and quantify the uncertainties. The uncertainties are combined using statistical methods to produce error band estimates. Preliminary results for catalytic liquefaction (PETC and LBL processes), gasoline from biomass (China Lake process), and MBG from wood, ethanol fermentation are reported here. A sensitivity analysis for co-generation is also reported.