A series of process design and economics models have been created which calculate the process cost for several scenarios in steam-explosion/fractionation of wood. Steam -explosion pulping may prove to be an alternative to currently practiced standard pulping processes which require large capital investments, cause significant environmental problems, and produce a narrow range of products. In addition, steam-explosion/fractionation technology may offer the opportunity to produce chemicals and materials from biomass at a lower raw material and process cost than the alternative petrochemical feedstocks. The models are a series of modular computer simulations, where each module summarizes a particular group of unit operations with respect to mass balance, energy requirements, and process cost including utilities, capital, labor, and other related costs. These modules are compiled into 3 groups of scenarios: 1) unprocessed steam-exploded wood for use as enzyme! acid hydrolysis feedstock, hardboard production, or as unbleached pulp, 2) water extracted steam-exploded wood for recovery of pentosan polysaccharides and a lignocellulosic fiber, and 3) water and aqueous solvent (alkali or ethanol) extracted steam -exploded wood for recovery of pentosan polysaccharides, lignin polymers, and a cellulose -rich, unbleached fiber. For the base case evaluated, the cost of producing a 50% moisture, based on total weight, steam-exploded fiber is the raw material cost, dry basis, plus 3.5 cents! Lb of raw material consumed, dry basis. For Southwestern Virginia hardwoods at 2 cents/Lb ($40 per ton), dry basis, the total process cost is 5.5 cents/ Lb. / Master of Science