The invention relates to a process for hydrolyzing cellulose, comprising: (a) contacting cellulose with a fluid mixture comprising supercritical CO.sub.2 and sub-critical or near-critical water to form a reactant mixture at a first temperature and first pressure for a first time period, wherein a reaction occurs and forms one or more hydrolysis products; (b) quenching the reaction; and (c) recovering at least one hydrolysis product.