The production of ethanol from corn fiber has the potential to increase ethanol yields by a maximum of 0.3 gal/bushel in a wet-milling process. Incremental yields would be 0.13 gal/bushel from hexose, 0.1 from D-xylose and 0.07 from L-arabinose, at 100% hydrolysis and fermentation efficiency. At 80% efficiency for hexose hydrolysis and fermentation and 70% for pentose, an incremental yield of 0.22 gallons/bushel of corn is expected Of this total, 0.1 gal/bushel would be from hexoses, 0.07 from D-xylose, and 0.05 from L-arabinose. A maximum practical incremental yield would probably fall between 0.22 and 0.3 gallons/bushel. bushel. These calculations are based on published compositional analyses of cellulose, starch, mono-sac charides, hemicellulose, protein and oil as distributed between the compartmentalized components of the corn kernel and published yield factors for hexose and pentose fermentations. Experimental yield factors for xylose (0.36 g ethanol/g xylose) and arabinose (0.34) fermenting microorganisms are lower than that for glucose (0.45-0.50), and significantly less than the theoretical yield of 0.51 g ethanol/g pentose. Nonetheless, we estimate that a wet-milling facility which currently produces 100 million gallons/year of ethanol from starch could generate an additional $4-8 million of annual income if the fiber components were processed into ethanol. Hence, advances in fiber pretreatment and pentose fermentation are likely to have a major impact on enhancing productivity of corn ethanol plants. An engineering framework for assigning economic consequences of the additional utilization of fiber is presented. Copyright (C) 1997 Elsevier Science Ltd.