The knowledge of the supramolecular structure of a polar oil that contains a bio-based extractant is necessary a deep understanding of solubilization processes of polar species in oils. In this contribution, we focus on a ternary system containing the polyglyceryl-3-diisostearate (PG3DS), a bio-based extractant in cosmetic formulation, methyl esters (ME-Cn) as model diluent and water. The realms of existence of monophasic regions were determined in the ternary phase diagrams varying the chain lengths, Cn, of the diluent between 7 and 14 carbons. We provide here for the first time fundamental information of the impact of the water content and of the organic diluent on the miscibility and aggregation properties of PG3DS in MEs. The structure of PG3DS aggregates in the monophasic region were accessed by combining small and wide angle X-ray scattering (SWAXS) experiments and molecular dynamics simulation. Though small, these aggregates can be considered as reverse micelle with a polar core made of a few water molecules, polar heads of PG3DS and few polar parts of the diluent which is the host for polar solutes, such as antioxidants, in an oleo-eco-extraction process.