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Hydrothermal liquefaction (HTL) is being investigated as a potential process to provide a renewable energy source from waste biomass. Organically rich wet waste can be partially converted to a renewable crude in subcritical water. Byproducts from HTL include solid, gaseous, and aqueous phases. As a result of the variations in the types of biomass that can be used as a feedstock for HTL, reaction products can vary significantly. To quantify the product distribution from HTL of biomass, the development of a process-based model is necessary. The organic fraction of biomass is typically made up of carbohydrates, lignin, lipids, and proteins. To quantify reaction kinetics, multivariate HTL experiments were performed with variable temperatures (250–350 °C) and times (0–60 min) on mixtures of model compounds representing the carbohydrate, lignin, lipid, and protein components of biomass. Previously, we have investigated the reaction kinetics of different monomer and polymer model compounds by reacting them alone. In this work, we report the investigation of mixtures of the model compounds as HTL reactants to determine the yields of crude, aqueous, gas, and solid phases. Interactions between different model compounds in experiments with mixtures resulted in variable yields compared to the mass-averaged yields from reactions with individual model compounds. From the relation of feed composition in the modeled HTL process to the observed fractions of products, the process conditions can be optimized to maximize the production of oil and a feedstock can be selected on the basis of its composition. Crude fractions from model biomass sources have been characterized via gas chromatography–mass spectrometry analysis.