Lignocellulosic wastes, including corn stalks and wheat straw, were pretreated and hydrolyzed with combined supercritical and subcritical hydrothermal technology. Soluble sugars were collected by pre-washing the crushed materials before hydrolysis. The effects of solid-liquid ratio, temperature, and reaction time on oligosaccharide production were investigated and the optimum supercritical conditions were found to be 20 mg/2.5 ml water, 384 degrees C, 17 s for corn stalks and 20 mg/2.5 ml water, 384 degrees C, 19 s for wheat straw. Subsequent subcritical processing of the hydrolyzate (with or without the water extract) from supercritical treatment was guided by a previous analysis of cellulose hydrolysis kinetics. The highest yield of fermentable hexoses from corn stalks (27.4% of raw material) was obtained at 280 degrees C, 27 s, and from wheat straw (6.7% of raw material) at 280 degrees C. 54 s. This study provides novel key parameters for fermentable hexose production from lignocellulosic feedstocks using combined supercritical and subcritical hydrothermal treatment. (C) 2009 Elsevier Ltd. All rights reserved.