This study investigated the optimum thermochemical liquefaction (TCL) operating conditions for producing biocrude from Spirulina platensis. TCL experiments were performed at various temperatures (200-380 degrees C), holding times (0-120 min), and solids concentrations (10-50%). TCL conversion at 350 degrees C, 60 min holding time and 20% solids concentration produced the highest biocrude yield of 39.9% representing 98.3% carbon conversion efficiency. Light fraction biocrude (B(1)) appeared at 300 degrees C or higher temperatures and represented 50-63% of the total biocrude. Biocrude obtained at 350-380 degrees C had similar fuel properties to that of petroleum crude with energy density of 34.7-39.9 MJ kg(-1) compared to 42.9 MJ kg(-1) for petroleum crude. Biocrude from conversion at 300 degrees C or above had 71-77% elemental carbon, and 0.6-11.6% elemental oxygen and viscosities in the range 40-68 cP. GC/MS of biocrude reported higher hydrocarbons (C(16)-C(17)), phenolics, carboxylic acids, esters, aldehydes, amines, and amides. (C) 2011 Elsevier Ltd. All rights reserved.