The development of a numerical simulation, based on cubic equations of state for blowdown of vessels containing high pressure hydrocarbons is described. The model＇s performance is evaluated by comparison with experimental data relating to the blowdown of a condensable hydrocarbon mixture in a full sized vessel at a starting pressure of 118 bar. Typical output data including lime-temperature profiles for the vapour and liquid phases as well as the wetted and unwetted walls are reported. These are shown to be within +/- 5 K of experimental data. In general, it is found that the choice of the cubic equation of state has little effect on the data.