Fatty acid methyl esters (biodiesel) were produced by the transesterification of triglycerides with compressedmethanol (critical point at 240 C and 81 bar) in the presence of solid acids as heterogeneous catalyst(SAC-13). Addition of a co-solvent, supercritical carbon dioxide (critical point at 31 C and 73 bar),increased the rate of the supercritical alcohols transesterification, making it possible to obtain high biodieselyields at mild temperature conditions. Experiments were carried out in a fixed bed reactor, andreactions were studied at 150–205 C, mass flow rate 6–24 ml/min at a pressure of 250 bar. The molarratio of methanol to oil, and catalyst amount were kept constant (9 g). The reaction temperature andspace time were investigated to determine the best way for producing biodiesel. The results obtainedshow that the observed reaction rate is 20 time faster than conventional biodiesel production processes.The temperature of 200 C with a reaction time of 2 min were found to be optimal for the maximum(88%) conversion to methyl ester and the free glycerol content was found below the specification limits.