Switchgrass is a North American grass that is considered to be a highly promising herbaceous bioenergy feedstock. Differences in processing conditions and yields specifically related to switchgrass cultivar or cytotype (upland or lowland) can be confounded by differences in harvest date or region of growth. For this research, AFEX (TM) pretreatment conditions and hydrolysis enzyme mixtures were statistically optimized for Alamo (lowland) and Shawnee (upland) switchgrass that had been harvested in December in Oklahoma. Optimal pretreatment conditions and enzyme mixtures were almost identical for both varieties and gave similar mass sugar yields. Inclusion of hemicellulases in the enzyme mixture maintained total sugar yields with 50% reduction in enzyme loading. Regardless of variety, the biorefinery should be able to obtain high sugar yields using the same pretreatment and hydrolysis conditions to process switchgrass grown under the same environmental conditions, in the same location, and harvested at the same time of the year. (C) 2011 Elsevier Ltd. All rights reserved.