Some advances in the technology applied in the design of olefins plants illustrate the extent to which flexibility serves to optimize energy consumption. Chemical processers planning to construct an olefins facility can now opt for a flexible feedstock slate. Once the flexibility is incorporated into plant design, whatever feedstock is optimal at a given time can be used. Operating efficiency can be further maximized by the use of computerized controls programmed to monitor the amount of energy input consumed per unit of output.