Progressive depletion of world oil resources, combined to increasing energy consumption as well as the negative environmental impact of fossil fuel use, led to a shift toward alternative renewable sources of energy. Biodiesel is among the most viable liquid transportation fuels for the foreseeable future, with the potential of contributing significantly to sustainable development in terms of socioeconomic and environmental concerns. Indeed, biodiesel is a mixture of alkyl esters obtained by transesterification (alcoholysis) of triglycerides from vegetable oils or animal fats with an alcohol (methanol or ethanol). The transesterification reaction is commonly carried out in the presence of a catalyst the main drawback of which is to be water sensitive, preventing the use of non-conventional feedstocks (such as waste cooking oils or algal biomass) [1]. Emerging non- catalytic alcoholysis methods based on supercritical fluids allow solving this problem. Nevertheless, their industrial scale application is limited because of the severe operating conditions required (high temperature, high pressure, and high alcohol to oil molar ratio) which can be successfully reduced by addition of a co-solvent, such as CO 2 [2 -4]. To optimize the supercritical process via simulation, the phase behaviour under high temperatures and pressures for systems containing CO 2 and components involved in biodiesel production must be firstly investigated...