We examined the gasification of biomass in supercritical water and the esterification of oleic acid in supercritical ethanol. Cellulose and lignin were converted to gases rich in H2 and CH4. Both the gas yield and its composition were sensitive to changes in the gasification temperature, the biomass loading, and the water density. Additionally, metal catalysts can be used to obtain further control of the rate and selectivity of the gasification reaction. Esterification of free fatty acids by alcohols is one step in an envisioned catalyst-free process for biodiesel production from triglycerides. The esterification proceeded smoothly in supercritical ethanol, and we examined the effects of the process variables on the kinetics and ester yields. The processes noted above are but two that illustrate the usefulness of supercritical fluids for biomass processing.