Liquefaction is a process of converting biomass into a bio-oil in the presence of a solvent— usually water, an alcohol, or acetone—and a catalyst [22]. Liquefaction operates at milder temperatures than gasification, but requires higher pressures. Liquefaction can be indirect, wherein biomass is converted into gas and thence into liquid, or direct, in which biomass is converted directly into liquid fuel [23]. Bio-oils produced in direct liquefaction processes usually produce heavy oils with high heating values and value-added chemicals as by-prod­ucts. Direct liquefaction also produces relatively little char compared to other thermochemi­cal processes that do not utilize solvents. In addition, liquefaction has the advantage that the method is not hindered by the water content of the biomass, giving credence to utilizing this method for water based biomass. The use of water as a solvent can significantly reduce op­erating costs, and recent studies with sub-and super-critical water have demonstrated in­creased process productivity by overcoming heat-transfer limitations [24, 25]. Operating parameters and feed quality significantly influence the overall quality of the oil produced by these processes. A recent review presented an exhaustive comparison of the operational var­iables that affect the liquefaction of biomass and concluded that a well-defined temperature range is the most influential parameter for optimizing bio-oil yield and biomass conversion [22]. Similarly, catalyst choice can alter the heating value of the final liquefaction product and reduce the quantity of solid residue [25].