EROI and The Net Energy Cliff

EROI is measures the fundamental idea that the less energy you need to invest to get energy in return, the more will be left over for society to do other things that keeps civilization going.

Two-axis graph, showing % of net energy out as a function of EROI. EROI starting at 50 and declining precipitously below EROI of about 5
Net Energy Cliff, with EROI expressed as the number on the horizontal axis. (Lambert et al.)