In 2005 the USDA and DOE jointly published a report concluding that it would be technically feasible to supply a billion dry tons of biomass annually from farms and forests throughout the United States in support of an emerging bioenergy and bioproducts industry. The report was criticized because it defined 'supply' largely in terms of physical availability without a formal evaluation of economic feasibility. As a result, during 2008 and early 2009 the two agencies conducted a follow-up study in an effort to assess the potential biomass supply economically by deriving county-level supply curves for farm and forest biomass. This paper describes the forest harvesting model that was used to estimate costs associated with collecting and preparing forest biomass for transport to processing facilities. The model was updated from an earlier version that was limited to forest conditions in the Interior West. The revised model has been designed for use in all regions of the contiguous United States. Actual results from the study are not provided in this paper because they have not yet been cleared for release by the USDA and DOE.