Corn-stover feedstock costs were estimated for a proposed biomass-to-ethanol conversion facility in southern Minnesota, USA, accounting for county-specific yields and transportation distances, erosion constraints, machinery specifications, and transportation, storage, and densification costs. Monte Carlo simulation was used to estimate the probability distribution of costs under alternative assumptions on key parameters whose values vary widely in the literature. For a facility producing 0.189 hm(3)y(-1) of ethanol, marginal feedstock cost was estimated at $60 Mg-1 ($200 m(-3) ethanol) for the more-intensive harvest method and $72 Mg-1 ($210 m(-3)) for the less-intensive method. Costs were greater than $68 Mg-1 ($240 m(-3)) for a facility producing > 0.757 hm(3) y(-1) ethanol under the more-intensive method, and greater than $93 Mg-1 ($320 m(-3)) for the less-intensive method. Monte Carlo simulation estimated a mean marginal cost of $57 Mg-1 ($69 Mg-3 under the less-intensive harvest method) for 0.189 hm(3) ethanol output, with a $12 ($10) standard deviation. Costs were found to be at or below $68 Mg-1 90 percent of the time ($78 Mg-1 for the less-intensive method). A $12 Mg-1 standard deviation in stover cost would result in a $40 m(-3) swing in ethanol cost. (C) 2007 Elsevier Ltd. All rights reserved.