Peak oil does not occur when we run out of oil. Peak oil occurs when the marginal consumer is no longer willing to pay the cost of extracting and processing the marginal barrel of oil. And we can actually calculate what the related numbers are.
To begin with, we refer to the price a nation’s oil consumers are willing to pay as its “carrying capacity.” For the US, carrying capacity is about $95-100 Brent [per-barrel oil price in London]. If the oil price is above this level, oil consumption will decline—which is exactly what we see and what we predicted four years ago. But carrying capacity is not a static number. It changes over time, specifically, with three things: GDP growth, efficiency gains in the use of oil, and dollar inflation. So if GDP goes up, efficiency goes up and the CPI goes up, then the amount that consumers are willing to pay for oil will increase. For China, by the way, we estimate the carrying capacity at around $115-120 / barrel Brent. So oil consumption will increase in China at $115 Brent, but fall in the advanced economies—exactly the pattern we’ve seen in the last few years.
Interview with Steve Kopits - capital expenditures in the oil industry