Different synthetic glucose/xylose mixtures (60 g/L total sugar) were fermented into ethanol using R stipitis CBS 6054. Glucose was the preferred substrate in the glucose/xylose mixtures. The high glucose fractions had higher cell biomass production rate and therefore higher substrate consumption rate and ethanol production rate compared to high xylose fractions. However, the high xylose fractions had a slightly higher ethanol yields compared to the high glucose fractions because the substrate was channeled into ethanol production rather the cell biomass. The maximum ethanol concentration was 22.7 and 24.3 g/L in 60 g/L glucose and xylose media, respectively. Using the same initial cell concentration of 2 g/L, fermentation was complete after 96 h of fermentation in 100% glucose (60 g/L), and after 120 h of fermentation in 100% xylose (60 g/L). (c) 2006 Elsevier Ltd. All rights reserved.