Molar volumes of molten indium have been measured in an isothermal compression up to 8.5 GPa at 710(3) K in an externally heated diamond anvil cell. The measurement is based on the x-ray diffraction and x-ray absorption of materials using a synchrotron monochromatic x-ray microbeam. The fit to the results with the Birch–Murnaghan equation of state gives parameters of V0 = 16.80 cm3, K0 = 23.9(6) GPa, assuming that K′ = 4. This method should be applicable for measuring molar volumes of liquids and other amorphous materials in the diamond anvil cell. © 2002 American Institute of Physics.