An apparatus for the automated measurement of the densities of compressed liquids over the temperature ran-e of 270-470 K with pressures to 50 MPa is described. The heart of the apparatus is a commercial vibrating-tube densimeter. To minimize the uncertainty in our measurements, several physical and procedural improvements have been implemented beyond that of the commercial instrument operated in a stand-alone mode. The apparatus was designed, and software has been written, so that the operation and data acquisition are fully automated. The densimeter was calibrated using measurements under vacuum, as well as in propane and toluene, over the temperature and pressure ranges of the apparatus. Performance measurements on dimethyl ether are reported from 270 K to 470 K, up to pressures of 46 MPa, with an uncertainty of 0.64-0.81 kg/m(3).