Pairs of ionic liquids with the chloride or acetate anion as common ion and with largely different cations (namely a 1-alkyl-3-methylimidazolium cation and either methyltrioctylammonium or trihexyl(tetrade cyl) phosphonium) were selected to investigate their mutual miscibility. Most of the pairs investigated were found to give rise to biphasic, non-volatile, totally liquid systems over wide temperature and composition ranges. An accurate determination of the liquid-liquid equilibria was carried out as a function of temperature, finding LCST-like behaviours for the systems with the phosphonium cation, and hourglass-shaped liquid-liquid domains for the systems with the ammonium cation. Enthalpies and entropies of mixing, calculated from the liquid-liquid equilibrium values, revealed that the first type of liquid-liquid equilibria was entropically driven, whereas for the second type a transition from enthalpically to entropically driven occurred with an increase in temperature. (C) 2016 Elsevier Ltd.