We developed a general kinetic model for hydrothermal liquefaction (HTL) of microalgae. The model, which allows the protein, lipid, and carbohydrate fractions of the cell to react at different rates, successfully correlated experimental data for the hydrothermal liquefaction of Chlorella protothecoides, Scenedesmus sp., and Nannochloropsis sp. The model can faithfully account for the influence of time and temperature on the gravimetric yields of gas, solid, biocrude, and aqueous-phase products from isothermal HTL of a 15 wt% slurry. Examination of the rate constants shows that lipids and proteins are the major contributors to the biocrude, while other algal cell constituents contribute very little to the biocrude. (C) 2014 Elsevier Ltd. All rights reserved.