The current paper extends the application of the overall design methodology for sub-ambient plants, developed by Dhole and Linnhoff (1993a), to optimise the operating pressure of the ethylene cold-end process. The optimisation of the working pressure depends on the trade-off between the power required for refrigeration and for feed compression. Appropriate integration between the columns, the heat exchanger network and the refrigeration system significantly reduces the overall power consumption. More importantly, the optimised process configuration shows a small variation in total power consumption with operating pressure. This implies that with appropriate integration, the low pressure designs become more attractive owing to the lower capital investment required. Lower operating pressure along with process integration can also be considered as a debottlenecking tool when the separation system is the main constraint.