Based on optimized pretreatment process, oil palm fronds (OPFs) were sequentially pretreated with 1.4% (w/v) aq. NaOH in 80% ethanol with ultrasound assistance (at 75 degrees C for 30 min) and 3% (v/v) aq. H2O2. Using the Box-Behnken design (BBD) of response surface methodology (RSM), bioethanol production from the sono-assisted organosolv/H2O2 OPFs were optimized using same-vessel enzymatic saccharification and fermentation (SVSF) where both the hydrolysis and fermentation processes were carried out in one vessel simultaneously. Throughout the SVSF process, the incubation time and enzyme loading were kept at 72 h and 15 filter paper unit (FPU)/g substrate respectively. The other SVSF parameters which affect bioethanol yield such as temperature (X-1: 30-50 degrees C), solid loading (X-2: 5.0-10.0% w/v), yeast concentration (X-3: 5.0-20 g/l) and pH (X-4: 4.0-7.0) were optimized. Well fitted regression equations (R-2 > 0.97) obtained were able to predict reliable optimum bioethanol concentration and yield. The predicted optimum bioethanol concentration (i.e., 20.61 g/l) and yield (i.e., 84.60%) were attained at 36.94 degrees C (similar to 37 degrees C), 7.57% w/v solid loading (similar to 8.0% w/v), 13.97 g/l yeast concentration (similar to 14.0 g/l) and pH of 5.29 (similar to 5.30). Validated results indicated a maximum ethanol concentration and yield of 21.96 g/l and 84.65% respectively, which were closer to the predicted optimum responses. Using the optimum conditions, the highest bioethanol productivity of 0.76 g/l/h was observed at 12 h of SVSF process. (C) 2013 Elsevier Ltd. All rights reserved.