There would be no surplus if EROI approaches 1:1. Hall showed that the real cutoff is well above that, estimated to be 3:1 to sustain the essential overhead energy costs of a modern society. The EROI of the most preferred energy source, petroleum, has fallen in the past century from 100:1 to the range of 10:1 with clear evidence that the natural depletion curves all are downward decay curves. An EROI of more than ~3, then, is what appears necessary to provide the energy for socially important tasks, such as maintaining government, legal and financial institutions, a transportation infrastructure, manufacturing, building construction and maintenance and the lifestyles of all members of a given society.