Thermodynamic properties of a condensate gas have been measured in a large range of temperatures and pressures. Volumetric properties, liquid drop-out curves at constant mass, and dew pressures have been determined at 314, 353 and 393 K. Isobaric heat capacities have been measured along five isobars from 30 MPa to 40 MPa and sound velocities have been determined in a temperature range from 293 K to 373 K and in a pressure range from 40 MPa to 100 MPa. The behaviour of condensate gas investigated has been predicted using a thermodynamic model based on the Peng-Robinson equation of state. Tuning the model has been performed by selecting a pseudo-ternary hydrocarbon mixture equivalent to the C-11 + fraction and predicting correctly the liquid drop-out curve and the dew point pressure at 314 K.