Lime pretreatment has demonstrated advantageous to importantly increase the digestibility of lignocellulosic biomass with little or no degradation of sugars. It has been amply studied at gentle conditions (up to 65°C and atmospheric pressure for 1 to 4 weeks) and more severe conditions (up to 180°C and 300 psig pressure with oxygen for 1 to 10 hours). However, no data has been recorded for short pretreatment at pretreatment times less than an hour. In this work, lime pretreatment is used on switchgrass and pine covering a temperature range between 100 and ~250°C using oxygen and pretreatment times between 5 min and 6 hours.