Densities of compressed liquid ethane-propane mixtures are reported at five temperatures between 10. 00 and 48. 90 degree C. For each isotherm the data cover eight compositions ranging between 30 and 95 mol% ethane at pressures up to 9. 65 MPa. The excess volumes derived from the data are negative, extremely dependent on temperature and pressure, and can represent up to a 50% correction to the ideal mixture volume.