Background/Question/Methods
We review life cycle analyses (LCAs) of biofuel production and explore the points of debate that drive controversy over whether or not biofuels offer a more positive energy balance than fossil fuels. There is very little agreement among studies that attempt to quantify the energy balance of biofuels. Carbon dioxide fluxes to the atmosphere that are associated with grass-derived ethanol production have been estimated to be low enough to displace 114% of fossil fuel CO₂ emissions but other estimates suggest that CO₂ emissions associated with grass-derived ethanol are 43% greater than CO₂ emissions from fossil fuel use. Future research in bioenergy depends on resolving sources of error in interdisciplinary LCAs that generate such wide ranging estimates.

Results/Conclusions
We identified three components of LCAs that are the probable cause for the wide variance in net energy values and greenhouse gas emissions that have been published for biofuels: (1) variable energy efficiency definitions, (2) variable life cycle inventories, and (3) variable system boundaries. Life cycle analyses of energy systems require feedbacks from sub-systems that are defined by specialists in diverse fields and standardized methods are key to achieving comparable and meaningful results. It is imperative that we work toward defining the ecological factors that may change within the economic and political infrastructure that is already pushing biofuel production forward.