In this study, ethanol organosolv pretreatment was investigated and optimized for the pretreatment of empty palm fruit bunch using (1) response surface methodology based on three-variable central composite design and (2) the combined severity parameters. The reaction parameters studied were sulfuric acid concentration (0.5-2.0%), reaction temperature (160-200 degrees C) and residence time (45-90 mm). Both models provide valuable and complementary informations: using combined severity parameters, very good predictions were obtained concerning xylan and lignin extraction whereas central composite design is the best model for glucose production. The optimal values of the variables were as the followings: sulfuric acid 2.0% w/w, 160 degrees C, 78 min and the experimental values (96.0%) concerning glucose and lignin recovery were in excellent agreement with the central composite design prediction (100%). (C) 2011 Elsevier Ltd. All rights reserved.