Year in review--EROI or energy return on (energy) invested.

There have been five foremost empirical efforts regarding energy return on investment (EROI) analysis over the past few years, including the topics of: (1) whether corn ethanol is a net energy yielder; (2) a summary of the state of EROI for most major fuel types; (3) alternative applications of EROI, such as energy return on water invested (EROWI); (4) the relation between EROI and the economy; and (5) an attempt to calculate the minimum EROI for a sustainable society. This paper offers a review of these five main areas of interest and provides a history of the development of EROI as well as a review of some of the various definitions of EROI and how they apply to EROI analyses. The paper concludes by listing numerous areas of improvement that are needed within EROI research.