Energy in, energy out
‘Oil production is predicted to drop by over 50% in two decades’This means that more energy must be invested to maintain output. As a rough comparison, conventional crude oil production has an EROEI in the range 10–20:1, while tight oil comes in at 4–5:1. Oil recovered from (ultra)deepwater drilling gives 4–7:1, heavy oil 3–5:1, and oil shale (kerogen) somewhere around 1.5–4:1. Tar sands is around 6:1, if it is recovered by surface mining, but this falls to around 3:1 when the bitumen is ‘upgraded’ by conversion to a liquid ‘oil’ substitute.