Simultaneous supercritical extraction and transesterification (SET) process is a novel biodiesel production process for oil seeds in which the solid oil-bearing material is used as the primary reactant together with short-chain alcohol directly in supercritical condition. In this experimental work, SET process with methanol was carried out in a high-pressure batch reactor to produce fatty acid methyl esters (FAME) from Jatropha curcas L. seeds (15.0 g feed, 300 degrees C, 5.0 ml/g methanol to solid ratio and 30 min). Different types of co-solvents (pentane, heptane, toluene, tetrahydrofuran, nitrogen and carbon dioxide) with varying amount (1.0-5.0 mug for liquid and 10-50 bar for gas) were added into the process to study their influences towards the extraction efficiency, E-y and FAME yield, F-y. It was found that pentane and CO2 provided higher responses (E-y: 102.6% and 107.0%, F-y: 100.4% and 102.3%) at concentration of 1.0 ml/g and 50 bar respectively. Addition of pentane and CO2 was also discovered to lower the critical conditions of the reactant mixture and could achieve near optimum product yield at lower temperature (280 degrees C) and lower methanol to solid ratio (4.0 ml/g). Addition of appropriate co-solvents could increase the extraction rate (solid-liquid) and enhance methanol-oil inter-phase miscibility during the reaction phase. This proved that SET process can be rather promising as another alternative route for biodiesel production. (C) 2013 Elsevier B.V. All rights reserved.