Corn stover, the inedible leaves, stalks, and cobs, is a large, currently available source of cellulosic biomass.  Understanding the feedstock composition and variability is critical to developing economic biomass to transportation fuels and chemicals processes.  At the National Renewable Energy Laboratory (NREL), corn stover has been a model feedstock for developing a biomass to ethanol process.  We will report on the results of a multi-year effort aimed at surveying the entire range of corn stover compositions.  A near infrared (NIR) based rapid analysis method was used to predict the biomass composition of thousands of corn stover samples.  These samples cover a range of growing locations, harvest years, and plant varieties.  We will report the “average” corn stover composition and discuss why samples with the average composition are not seen.  We also will discuss the wide compositional ranges seen, and their possible effect on the biomass to ethanol conversion process.