In order to obtain new insights into the molecular-level mechanisms behind the polymer based aqueous biphasic systems (ABS) formation, phase equilibria including both liquid-liquid and vapor-liquid equilibria of different aqueous polymer-carbohydrate systems was deeply scrutinized in this work. For this purpose, the relative ability of a large range of mono-, di- and trisaccharides, as well as polyols to form ABS with different water soluble polymers PPG400, PPG725, PEG400, PEG4000 and PEG10000 was investigated at different temperatures. It was found that, the ABS formation seems to be controlled by the interplay of the relative strength of the carbohydrate-water, polymer-water and carbohydrate-polymer interactions. In the case of aqueous PPG + carbohydrates systems, because of the unfavorable PPG-carbohydrate interactions, the solutes exclude themselves from the vicinity of each other and therefore ABS are entropically formed when PPG and carbohydrate are mixed above a given concentration in an aqueous media. These systems show the negative deviation from the semi-ideal behavior. By increasing temperature and PPG molecular weight (PPG-water interactions become weaker) and increasing hydrophilicity of the carbohydrate (stronger carbohydrate-water interactions) the immiscibility region increases. However, in the case of PEG + carbohydrate aqueous systems which not capable of inducing phase separation, because of the favorable PEG-carbohydrate interactions, the interaction of each solute with water molecules becomes weaker in the presence of the other solute. Therefore the vapor-liquid equilibria behavior of these systems shows the positive deviations from the semi-ideal behavior. By increasing the PEG molar mass as well as the hydrophobicity of carbohydrate, the carbohydrate-PEG interaction increases and then the positive deviations from the semi-ideal behavior increase. (C) 2016 Elsevier Ltd. All rights reserved.