Figure 2. Metrics for evaluating ethanol based on the intensity of primary energy inputs (MJ) per MJ of fuel and of net greenhouse gas emissions (g CO2-equivalent) per MJ of fuel.

Net Fossil Inputs Net Fossil Ratio Petroleum Input GHG Emissions
MJfossil needed for each MJfuel MJfuel produced for each MJfossil input MJpetroleum needed for each MJfuel g CO2-equivalent per MJfuel**
Gasoline 1.19 0.84 1.10 94 
Ethanol Today 0.774 1.30 0.04 77*
CO2 Intensive Ethanol 0.94 1.06 0.18 91*
Cellulosic Ethanol 0.10 10.0 0.08 11 
MJ = Mega Joule, an energy unit. *These values are highly uncertain and may be greater than gasoline-related emissions. **GHG emissions include combustion.

Notes: Current agricultural production creates soil erosion, nutrient runoff, and other environmental impacts that cannot be accurately represented in energy units. Progress toward attaining energy and environmental goals will require new technologies and practices, such as sustainable agriculture and cellulosic ethanol production. In addition, the conversion of land to agriculture for ethanol production also has environmental consequences.

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1Energy and Resources Group, 2Goldman School of Public Policy, 3Renewable and Appropriate Energy Laboratory, University of California, Berkeley