The ESPI measures the maximum feasible saving potential compared
with the best-performing firms and reflects the inefficiency level with
respect to the energy factor. The value of the ESPI is non-negative and
less than or equal to 1. A higher value of the ESPI indicates a larger inefficiency and a greater potential to remove excessive energy input
through efficiency improvement. It should be noted that a zero value
of the ESPI does not imply that the firms are perfect and without any excessive energy or inefficiency during the production process. Rather, it
indicates that the firms are Pareto–Koopmans efficient among all of
the observations in the sample (Charnes et al., 1985)