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The cost of cellulase enzymes has limited the feasibility of producing ethanol from fibrous biomass. Traditional submerged fermentation (SmF) was compared to an alternative method of producing cellulase, solid state cultivation (SSC). Results from an economic analysis indicated that the unit costs for cellulase enzyme production were $15.67 (The prices are all 2004 prices in this article, except otherwise stated. We deflated newer prices to 2004 prices using a deflation factor 0.9 per year and inflated older prices to 2004 prices using an inflation factor 1.1.) per kilogram ($/kg) and $40.36/kg, for the SSC and SmF methods, respectively, while the corresponding market price was over $90.00/kg. A sensitivity analysis conducted using Monte Carlo simulation also suggests that the unit cost of production using the SSC method is lower than the unit cost of production using SmF with a certainty of 99.6% (9,959 out of 10,000 cases). These results indicate that the SSC method may be a more economical method of cellulase production, thereby reducing bio-ethanol production costs. SSC may increase the potential that bio-ethanol will become a viable supplemental fuel source in light of current economic, political, and environmental issues.