EROI estimates from three sources, Gagnon et al. , Cleveland  and Guilford et al. . The Gagnon et al.  data represent estimates of the EROI for global oil and gas production using aggregation by Divisia indices. The Cleveland  data represent the trend in EROI values for US oil and gas production calculated using the Divisia indices to aggregate energy units. The Guilford et al.  data represent estimates of the EROI of US oil production from 1919 to 2007.
The ‘net energy cliff’ graph, showing the relation between net energy and EROI. As EROI declines, the net energy as a percentage of total energy extracted declines exponentially. Note that the x-axis is in reverse order. (Adapted from Mearns .)
(a–d) Flow diagrams relating net energy, EROI and gross energy production for a hypothetical Economy A. Each diagram describes the energy flows according to a different EROI, where the EROI is (a) 10, (b) 5, (c) 2 and (d) 1.5.
The GERR as a function of declining EROI. In this example, the reference EROI was 11. As such, the GERR value associated with an EROI of 4 represents the proportional increase in gross energy required to deliver one unit of net energy if society transitioned from an energy source with an EROI of 11 to one with an EROI of 4.