Technical Abstract: Pretreatment of orange processing waste (CPW) by steam explosion under various conditions (pretreatment time, pH and temperatures) was investigated. Pretreatments longer than 4 min with steam purging resulted in CPW containing less than 0.1% limonene, an inhibitor for fermentation. Steam pretreatments for 2-6 min at 160 ºC with rapid decompression (steam explosion) broke down peel tissues, solubilized 90% of the hemicelluloses and 70% of the pectin in natural CPW. Addition of 0.6% phosphoric acid to pretreat CPW at pH 2.8 increased pectin solubility to better than 80%, but did not significantly increase the total dissolved solids until pretreatment times exceeded 6 min. Pretreatments at 160 ºC with addition of sodium carbonate to increase CPW initial pH to 6.8 and 8.2 destroyed 50% of the pectin and galacturonic acid after just 2 min, had significantly lower dissolved solids, and resulted in excessively viscous products. Total sugars fermentable by Saccharomyces cerevisiae were not changed after pretreatments at 160 ºC for up to 8 min on CPW between pH 2.2-8.2. Ethanol yields following 48 hr simultaneous saccharification and fermentations (SSF) ranged from 76 to 94%. Ethanol yields were slightly lower but not statistically significant in base modified pretreatments.