Energies 2009, 2, 25-47; doi:10.3390/en20100025
energies
ISSN 1996-1073
www.mdpi.com/journal/energies
Review
What is the Minimum EROI that a Sustainable
Society Must Have?
Charles A. S. Hall *, Stephen Balogh and David J. R. Murphy
Program in Environmental Science, State University of New York - College of Environmental Science
and Forestry, Syracuse NY, 13210, USA
* Author to whom correspondence should be addressed; E-Mail: chall@esf.edu
Received: 12 December 2008; in revised form: 10 January 2009 / Accepted: 13 January 2009 /
Published: 23 January 2009
Abstract: Economic production and, more generally, most global societies, are
overwhelmingly dependant upon depleting supplies of fossil fuels. There is considerable
concern amongst resource scientists, if not most economists, as to whether market signals
or cost benefit analysis based on today’s prices are sufficient to guide our decisions about
our energy future. These suspicions and concerns were escalated during the oil price
increase from 2005 – 2008 and the subsequent but probably related market collapse of
2008. We believe that Energy Return On Investment (EROI) analysis provides a useful
approach for examining disadvantages and advantages of different fuels and also offers the
possibility to look into the future in ways that markets seem unable to do. The goal of this
paper is to review the application of EROI theory to both natural and economic realms, and
to assess preliminarily the minimum EROI that a society must attain from its energy
exploitation to support continued economic activity and social function. In doing so we
calculate herein a basic first attempt at the minimum EROI for current society and some of
the consequences when that minimum is approached. The theory of the minimum EROI
discussed here, which describes the somewhat obvious but nonetheless important idea that
for any being or system to survive or grow it must gain substantially more energy than it
uses in obtaining that energy, may be especially important. Thus any particular being or
system must abide by a “Law of Minimum EROI”, which we calculate for both oil and
corn-based ethanol as about 3:1 at the mine-mouth/farm-gate. Since most biofuels have
EROI’s of less than 3:1 they must be subsidized by fossil fuels to be useful.
Keywords: Law of Minimum; EROI; economies; break-even, net energy, depletion.
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