Filtered WVO and methanol were loaded into the reactor with specified mole ratio. Then the batch reactor was submerged into the silica oil bath (6). In order to purify and liquefy, CO2 was passed through the filter (2) and condenser (3), respectively. Then, CO2 was charged to the high pressure pump (4) and to the batch reactor (5). The cooling liquid in the condenser was mixture of 50% (v/v) water and ethylene glycol. At this stage the back pressure regulator (7) was completely closed and pressure inside the reactor was increased up to the prescribed value. In this study adding the CO2 to the reactants not only cause to increase in the reactor pressure but also acts as a co-solvent. After the temperature and pressure of reactants were reached to the set values and transesterification reaction was carried out in the selected time, back pressure regulator was opened and reactor contents were discharged to the ice-water bath (9) and cooled rapidly to terminate the reaction. CO2 can be recycled and used again in the process. An electrical heater (8) was used on the tubing to prevent the Joule–Thompson effect for CO2.