Cellulose and corn stover were subjected to a reaction with polar cosolvents (methanol and water)/CO2 at subcritical and supercritical conditions. Resulting products from a cellulose reaction at 300oC analyzed by GCMS consisted of a mixture of organic acids, sugars, and several other components. Examples of organic acids included acetic, hexanoic, heptanoic and malonic acids, whereas sugars were levoglucosan, D-Allose, and D-Galactose. Furthermore product samples from a corn stover reaction at 300°C suggested presence of ketones, aromatic hydrocarbons, and methyl esters. As evidenced by these results, reactions at high pressure are plausible although they are accompanied by a complex product composition, and an unreacted residue of cellulose and lignin.