An experimental system for the determination of density, ultrasonic velocity and phase equilibria over a wide range of pressures was developed. Its particular characteristic is that it is well adapted to the investigation of single phase systems including both liquid and gaseous components under normal conditions of pressure and temperature. To extend knowledge of density to pressures above the experimental domain, a numerical procedure based on the use of ultrasound data was adapted from Davis and Gordon’s procedure (J. Chem. Phys., 46 (1967) 2650). The aim of this paper is to present results produced using the techniques and method developed in the case of a binary mixture of nitrogen and octane between its saturation pressure and 100 MPa.