Results and Conclusions
The thermal equivalent and Divisia EROI for petroleum extraction show significant differences
(Fig. 2). The quality-corrected EROI declines faster than the thermal-equivalent EROI. The thermal - equivalent EROI increased by 60% relative to the Divisia EROI between 1954 and 1992. This difference was driven largely by changes in the mix of fuel qualities in energy inputs. Electricity, the highest quality fuel, is an energy input but not an energy output. Its share of total energy use increased from 2 to 12% during the period; its cost share increased from 20 to 30%. Thus, in absolute terms the denominator in the Divisia EROI is weighted more heavily than in the thermal-equivalent EROI. The Divisia-weighted quantity of refined oil products is larger than that for gas and coal. Thus, the two highest quality fuels, electricity and refined oil products, comprise a large and growing fraction of the denominator in the Divisia EROI compared to the thermal-equivalent EROI. Therefore, the Divisia denominator increases faster than the heat-equivalent denominator, causing EROI to decline faster in the former case.