Biomass is a primary source of renewable carbon that can be utilized as a feedstock for biofuels or biochemicals production in order to achieve energy independence. The low bulk density, high moisture content, degradation during storage and low energy density of raw lignocellulosic biomass are all significant challenges in supplying agricultural residues as a cellulosic feedstock. Torrefaction is a thermochemical process conducted in the temperature range between 200 and 300 degrees C under an inert atmosphere which is currently being considered as a biomass pretreatment. Competitiveness and quality of biofuels and biochemicals may be significantly increased by incorporating torrefaction early in the production chain while further optimization of the process might enable its autothermal operation. In this study, torrefaction process parameters were investigated in order to improve biomass energy density and reduce its moisture content. The biomass of choice (corn stover) was torrefied at three moisture content levels (30%, 45% and 50%), three different temperatures (200, 250 and 300 degrees C), and three unique reaction times (10, 20 and 30 min). Solid, gaseous, and liquid products were analyzed, and the mass and energy balance of the reaction was quantified. An overall increase in energy density (2-19%) and decrease in mass and energy yield (3-45% and 1-35% respectively) was observed with the increase in process temperature. Mass and energy losses also increased with an increase in the initial biomass moisture content. (C) 2011 Elsevier Ltd. All rights reserved.