The effects of AFEX (TM) pretreatment, feedstock moisture content (5,10, and 15 % wb), particle size (screen sizes of 2, 4, and 8 mm), and extrusion temperature (75, 100, and 125 A degrees C) on pellet bulk density, pellet hardness, and sugar recovery from corn stover, prairie cord grass, and switchgrass were investigated. Pellets were produced from untreated and AFEX (TM) pretreated feedstocks using a laboratory-scale extruder. AFEX (TM) pretreatment increased subsequent pellet bulk density from 453.0 to 650.6 kg m(-3) for corn stover from 463.2 to 680.1 kg m(-3) for prairie cord grass, and from 433.9 to 627.7 kg m(-3) for switchgrass. Maximum pellet hardness of 2342.8, 2424.3, and 1298.6 N was recorded for AFEX (TM) pretreated corn stover, prairie cord grass, and switchgrass, respectively. Glucose yields of AFEX (TM) corn stover pellets, prairie cord grass, and switchgrass pellets varied from 88.9 to 94.9 %, 90.1 to 94.9 %, and 87.0 to 92.9 %, respectively. Glucose and xylose yields of AFEX (TM) pellets were not affected by the extruder barrel temperature and the hammer mill screen size. The results obtained showed that low temperature and large particle size during the extrusion pelleting process can be employed for AFEX (TM)-treated biomass without compromising sugar yields.