Densification of agricultural residues is a key step in a cost-effective, large-scale, biomass feedstock supply system. Lab-scale densification systems exist which can produce large-scale densified corn stover briquettes that measure between 220 and 420 mm in length and with an average bulk density of 190 kg/m3 (dry particle density of 460 kg/m3). MOG (material other than grain ) and pure cob briquettes produced similar lengths and dry particle densities of 424 kg/m3 and 421 kg/m3, respectively. Durability testing, utilizing a modified form of ASABE S269.4 (ASABE Standards, 2007) was conducted to determine the overall product quality associated with these densified briquettes. This publication describes experiments which quantified the durability or briquettes produced with different material types (corn stover, MOG, the chaff from a conventional corn harvest, and pure cobs) and material particle sizes (produced from a combine chopper, MOG, and a hammer mill with a 19-mm screen opening size). The durability rating varied with each of the main effect test parameters and produced a maximum 46% durability rating using pure cobs directly from a combine without additional size reduction. The durability rating was quite low for corn stover and MOG briquettes, and it was improved for pure cob briquettes. Biomass preprocessing in a hammermill significantly reduced durability due to a lack of fiber interaction throughout the large briquette.