According to this wiki site, which may be close or way off:
EROI (for US) Fuel
100.0 Hydro
80.0 Coal
35.0 Oil imports 1990
35.0 World oil production
30.0 Oil and gas 1970
20.0 Oil production
18.0 Oil imports 2005
18.0 Wind
14.5 Oil and gas 2005
12.0 Oil imports 2007
10.0 Natural gas 2005
10.0 Nuclear
8.0 Oil discoveries
6.8 Photovoltaic
5.0 Ethanol sugarcane
5.0 Shale oil
3.0 Bitumen tar sands
1.9 Solar flat plate
1.6 Solar collector
1.3 Biodiesel
1.3 Ethanol corn
High per-capita energy use has been considered desirable as it is associated with a high standard of living based on energy-intensive machines. A society will generally exploit the highest available EROEI energy sources first, as these provide the most energy for the least effort. With non-renewable sources, progressively lower EROEI sources are then used as the higher-quality ones are exhausted.
For example, when oil was originally discovered, it took on average one barrel of oil to find, extract, and process about 100 barrels of oil. That ratio has declined steadily over the last century to about three barrels gained for one barrel used up in the U.S. (and about ten for one in Saudi Arabia).[citation needed] [3] Currently (2006) the EROEI of wind energy in North America and Europe is about 20:1[4] which has driven its adoption.
Although many qualities of an energy source matter (for example oil is energy-dense and transportable, while wind is variable), when the EROEI of the main sources of energy for an economy fall energy becomes more difficult to obtain and its value rises relative to other resources and goods. Therefore the EROEI gains importance when comparing energy alternatives. Since expenditure of energy to obtain energy requires productive effort, as the EROEI falls an increasing proportion of the economy has to be devoted to obtaining the same amount of net energy.
Since the invention of agriculture, humans have increasingly used exogenous sources of energy to multiply human muscle-power. Some historians have attributed this largely to more easily exploited (i.e. higher EROEI) energy sources, which is related to the concept of energy slaves. Thomas Homer-Dixon [5] demonstrates that a falling EROEI in the Later Roman Empire was one of the reasons for the collapse of the Western Empire in the fifth century CE. In "The Upside of Down" he suggests that EROEI analysis provides a basis for the analysis of the rise and fall of civilisations. Looking at the maximum extent of the Roman Empire, (60 million) and its technological base the agrarian base of Rome was about 1:12 per hectare for wheat and 1:27 for alfalfa (giving a 1:2.7 production for oxen). One can then use this to calculate the population of the Roman Empire required at its height, on the basis of about 2,500-3,000 calories per day per person. It comes out
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