Abstract Hydrothermal gasification of woody wastes, pine tree and fir tree sawdust, was performed in a batch autoclave at 500 and 600 °C and a pressure range of 20.0–42.5 MPa with or without a 10 wt.% of K2CO3. The products in the gaseous state (H2, CO2, and CH4, CO, and C2–C4 compounds) and in the aqueous state (carboxylic acids, furfurals, phenols, aldehydes, and ketones) were analyzed by gas chromatography and high performance liquid chromatography. The produced gas amount and the hydrogen and methane yields were found maximized at 600 °C with the addition of K2CO3. The decreasing pressure promoted hydrogen yields while decreasing the methane yields. The aqueous product was mainly composed of acetic acid, formic acid, and little amount of hydroxyacetic acid in the group of carboxylic acids and 5-methyl furfural and 5 hydroxymethyl furfural as furfurals. Supercritical water gasification of wood wastes is promising as a source in the production of hydrogen and methane.