AbstractAqueous dispersions of multilamellar liposomes of pure lipids and binary lipid mixtures have been investigated by densitometry. It is shown that the employed mechanical oscillator technique is well suited to derive volumetric data of different lipid phases and to characterize the transitions between them. Transition temperatures, widths, volume changes and in some cases also the kinetics can be studied. — For binary lipid alloys temperature‐composition‐phase diagrams can be established. By analysing the thermal expansion a direct comparison with calorimetric data is possible. Finally, an example for a chemically induced phase separation is