Extracting energy is an energy consuming process. In initial days when oil was the only source of fuel, the calculation involved measuring the cans of oil extracted by using one can of oil. Different fuels are now compared using this term. Find out more here
The current debate now revolves around whether the peak oil theory is valid and is the shale oil production really the answer to peak oil crisis.
ERoEI is the answer to whether it is really sustainable to produce biofuels with an ERoEI of 1.3.
Mission Shunya 