Some applications of molecular simulations of phase equilibria are reviewed. It is shown that the conventional simulations techniques require too much cpu-time to simulate the phase behaviour of most systems of industrial interest. It is therefore essential to simplify the models or to develop novel simulation techniques. Examples of both approaches are discussed. Simulations are used to investigate the role of dispersive interactions in the phase behaviour of model polar fluids. A novel Monte Carlo technique is described which can be used to simulate the phase behaviour chain molecules. This technique is many orders of magnitude more efficient than the conventional techniques and allow us to determine, for example, the phase behaviour of long-chain alkanes at conditions where experiments are not feasible.