||Development of a biofuel industry based on biomass will require large quantities of cellulosic feedstock. Among the proposals for acquiring this feedstock, without impacting other land uses such as food or forage, is the use of up to 50% of Conservation Reserve Program (CRP) land. Our objective was to determine CRP biomass production in northwestern Oklahoma and record the harvest impact on plant species composition, plant growth, and soil characteristics. Six CRP sites were harvested on three dates, early August, early October, and postfrost, for three consecutive years, 2004, 2005, and 2006. Three sites were Old World bluestem (OWB; Bothriochloa spp.) and three sites were native mixed species (NM). Across all years and harvest dates OWB produced 3790 kg ha-1 and NM produced 1920 kg ha-1 of dry biomass. Maximum yields were obtained at the October harvest for both OWB (4170 kg ha-1) and NM (2180 kg ha-1). There was no observed change in species composition or soil characteristics. Among all species evaluated, nitrogen, neutral detergent fiber, carbon, and ash concentrations varied significantly. Within NM, production of dry biomass among native grass species differed and ranged from 213 g plant-1 for big bluestem (Andropogon gerardii Vitman) to 14 g plant-1 for sand lovegrass [Eragrostis trichodes (Nutt.) Alph. Wood]. Biomass production consistently declined at all sites and for all harvest dates over the three harvest years, but the greatest decline in yield was for OWB.