We demonstrate a route for the production of C-3 hydrocarbons from renewable biomass by the hydrothermal conversion of well known fermentation end products Specifically, the major Commercial C-3 hydrocarbons, propane and propylene, can be obtained from butyric acid and 3-hydroxybutyrate (3HB) in substantial yields and industrially relevant productivities by hydrothermal decarboxylation. Butyric acid decarboxylates in supercritical water to give propane as the major product at 454 degrees C and 25 MPa. 3HB Undergoes joint dehydration and decarboxylation in subcritical water to yield propylene at 371 degrees C and 25 MPa with yields of up to 48 mol %. Although catalysts may be found that increase yields and selectivities, these processes were demonstrated without any added heterogeneous catalysts, and have the further advantage of requiring no external H-2 source.