Biomass can be hydrolyzed to yield fermentable sugars through pretreatment, which is the primary and expensive step in conversion of biomass to bio-ethanol. Most of the pretreatment operates in batch mode, which is energy intensive, requires high capital, results in decomposition of hemicellulose, and formation of inhibitors. Considering these shortcomings, a novel biomass pretreatment method using an extruder could be a viable continuous one. This systematic study was undertaken to determine the effect of different biomass parameters such as moisture content, and particle size over a range of barrel temperature, screw speed and screw compression ratio. Statistical analyses revealed that all the independent variables had significant effect on sugar recoveries and torque requirement. Mathematical models to predict sugar recoveries from different biomass were presented. The optimal pretreatment conditions for corn stover, switchgrass, big bluestem and prairie cord grass were presented.