(this is my attempt to understand and summarize in less than 500 words, in order to make it accessible to as many people as possible, a very important issue I’ve read about in the sources quoted below. Comments and corrections are very welcome) EROI (energy return on energy invested) is the ratio between the energy available for the economy and the energy it takes to produce that energy. An EROI of 100:1 means that the world gets 100 KWh for every KWh consumed to extract, process and distribute oil, carbon or any other power source, including renewable ones.