The Importance of Energy Return on Investment

Not all energy sources are created equal in terms of energy return on investment — the amount of energy they produce for the amount spent to produce them.

energy return on investment - bar graph
These bars represent the estimated maximum energy return on investment of both renewables and fossil fuels. Oil's ratio has declined over time with the increased difficulty of bringing it to consumers. Note its EROI value in 1930, 1970, 2000, and 2005.
SOURCE: CHARLES A. S. HALL AND JOHN W. DAY JR./AMERICAN SCIENTIST, GRAPH: MATTHEW T. STALLBAUMER