A compact, semiautomated isochoric apparatus is described. This apparatus can be used to measure p-V-T properties, vapor pressures for pure compounds, and phase boundaries for mixtures at temperatures between 200 and 450 K and pressures up to 18 MPa. A highly reproducible diaphragm-type differential pressure transducer is an integral part of the isochoric cell, providing pressure measurement a precise to +/-0.01%. The precision of the temperature measurement is +/-0.001 K. A microcomputer controls the temperature, records measured temperatures and pressures, and processes and stores the information. The performance of the apparatus is tested by measurements of the vapor pressure and isochores for carbon dioxide.