To meet the energy goal set by the US Biomass Research and Development Technology Advisory Committee, by 2030 1 billion ton of lignocellulosic feedstock need to be provided in a sustainable manner. Biomass feedstock is particularly important, because it is the only current renewable source of liquid transportation fuel. Currently, crop residues such as corn stover and wheat straw and energy crops such as warm- and cool-season grasses are available as biomass feedstock. The chemical composition of biomass feedstock is variable from location to location and from species to species. Since different feedstocks react differently to pretreatment and feedstock quality directly influences process yield and economics. Therefore, feedstock composition becomes an important issue in the development of integrated conversion technology. Feedstock composition data of crop residues and energy crops were obtained from published data and analyzed for variations among feedstocks. Total structural carbohydrates (cellulose + hemicellulose) ranged from 53.4 to 80.1 for switchgrass, 51.3 to 75.4 for corn stover, and 55.2 to 76.7% for wheat straw, respectively. The range of composition values was larger between locations (environmental factors) than among species (genetic factors).