Dear Colleagues,

Various studies have been conducted over the past half-century on the qualitative assessment of the degree to which the use of our energy resources can actually contribute to society. Systems ecologist Howard T. Odum, known as the progenitor of a qualitative energy assessment, first advanced the concept of “net energy” in the 1970s, which is essentially the energy obtained from an energy source minus the energy used in its acquisition and concentration (the energy investment or energy cost). One way to mathematically express the net energy is the EROI (energy return on investment), which was defined by Charles A.S. Hall in the late 1970s and 1980s as the ratio of the total energy gained from an energy production process to the energy invested in its acquisition. The estimation of EROI can provide useful insight for examining the advantages and disadvantages of different fuels in the energy production process, and is constantly being improved in terms of the protocol for the calculation and the system boundary. On the other hand, there are still many challenges, such as data uncertainty, in EROI estimation. Many EROI studies have focused on oil and gas resources, which are the most important to every aspect of our society, and have concluded that the EROI for oil and gas has declined over the past one to two decades. Although in recent years, much attention has been paid to EROI estimation for renewable energy resources, the future EROI trends for renewable energy resources are very uncertain. Several studies imply that such a declining EROI may have a large impact on the world economy and quality of life.

This Special Issue provides an opportunity for the further discussion of the potential benefits and challenges of EROI-related studies. We welcome submissions from a wide range of contributors in any area of EROI.

Prof. Dr. Jun Matsushima
Guest Editor

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• energy return on investment (EROI)
• net energy analysis
• energy quality
• resource depletion
• biophysical economics