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Nature Energy

Under many scenarios, fossil fuels are projected to remain the dominant energy source until at least 2050. However, harder-to-reach fossil fuels require more energy to extract and, hence, are coming at an increasing ‘energy cost’. Associated declines in fossil fuel energy-return-on-investment ratios at first appear of little concern, given that published estimates for oil, coal and gas are typically above 25:1. However, such ratios are measured at the primary energy stage and should instead be estimated at the final stage where energy enters the economy (for example, electricity and petrol). Here, we calculate global time series (1995–2011) energy-return-on-investment ratios for fossil fuels at both primary and final energy stages. We concur with common primary-stage estimates (~30:1), but find very low ratios at the final stage: around 6:1 and declining. This implies that fossil fuel energy-return-on-investment ratios may be much closer to those of renewables than previously expected and that they could decline precipitously in the near future. Published energy-return-on-investment ratios for fossil fuels have not always been estimated at the final point of use. By including all energy required for processing and the supply chain, Brockway et al. find that fossil fuels might have final energy return close to renewables and susceptible to rapid further decline in the near future.

Estimation of global final-stage energy-return-on-investment for fossil fuels with comparison to renewable energy sources