The net energy cliff

Charles Hall, the father of the energy return on investment (EROI) concept, once told me that our current society would probably not be able to function if the EROI for the entire society slipped below five.

What does that mean? First, a quick review. It takes energy to get energy. EROI is a measurement of how efficient a process, an enterprise or a society is in obtaining energy. EROI is usually expressed in a ratio, say, 20 to 1. That would mean that the process being studied produced 20 units of energy for every one unit expended. As it turns out, that’s about what conventional crude oil returns.


Hall estimates that the United States is currently running on an EROI of just under 40 to 1. This looks like a fairly substantial margin of safety over the 5 to 1 that might lead to societal breakdown. But worrisome developments in the oil, natural gas and coal fields may send us rushing toward that figure.

A post earlier this year on The Oil Drum suggests that the EROI for natural gas in North America is dropping like a stone. This is, in part, reflected in the price of natural gas which is up fourfold in this decade. It is also reflected in the number of wells and the number of total feet drilled just to maintain production. We are having to drill faster and deeper just to stay even. The recent uptick in U. S. supplies may represent a small flattening of the EROI decline, but those supplies are the product of furious drilling and huge exploration expenditures.

Energy Bulletin