The kinetics of bioethanol production using mono- and co-cultures of Saccharomyces cerevisiae and Pichia stipitis with glucose, xylose, and glucose-xylose sugar mixtures were investigated. A MATLAB (R) program was formulated for simulation of experimental results in order to get predicted values of ethanol production and sugar consumption and for kinetic parameter estimation. Kinetic parameters implied less extent of substrate and/or product inhibition when the co-culture scheme of immobilized S. cerevisiae and free P. stipitis was employed for fermentation of mixed sugars. In addition, a high ethanol yield was achieved by applying this co-culture strategy to wheat straw hydrolysates.