What goes up must come down. All non-renewable resources eventually peak in their production – rising up to a high point to meet demand, then declining thereafter. Peaks can be single, double, or undulating plateaus – their form depends factors like economic conditions, new technologies, and new discoveries. While these factors can affect production (sometimes substantially), ultimately depletion will always win. Production of "non-renewable" resources never rises continually to high points right before they run out. How could that possibly happen? Yet that seems to be the prevailing mentality in industry and government.
When a resource peaks, it doesn't mean it will run out anytime soon. But since it is natural to take the more profitable easy pickings first, then what remains is more difficult and expensive to extract. Current price determines whether marginal deposits will be extracted profitably, or just be left in the ground. Vast oil deposits cannot be extracted, because of geological and technological limits. A ratio, EROEI (Energy Returned on Energy Invested) reveals that when less usable energy is gained than is consumed to produce a resource, then it is simply not worth it. The higher the ratio, the better.
Take oil for an example. Decades ago, many wells returned an EROEI of 100; little energy was required to draw out the black gold. Think of the “Beverly Hillbillies” when Jed’s bullet hits the ground and the oil spurts out effortlessly, and you sort of get the idea. Now fields might average an EROEI of around 20. Deep-sea wells have an EROEI of less than five. An example of marginal utility, combined with great economic and ecological cost, is tar sands, with a ratio of about three. That is literally scraping the bottom of the barrel.
The ultimate timing of tops can't be predicted, sort of like trying to time the stock market – though certain data analysis can give a very close idea. Peaks can only truly be seen in the rear view mirror, as it were. Calculating accurate reserve estimates is problematic, since not all nations or corporations divulge complete or accurate information. Some nations don't give any data.
The whole concept of resource peaks or "Hubbert's Curve" (named after its discoverer, M. King Hubbert) has its doubters – more ideological than scientific – among those who believe new deposits will always be available, and if not, then the market will find substitutes. But the unique energy-dense qualities of fossil fuels make replacing them nearly impossible. Resource peaks are now well documented in many places, so the concept has squarely moved beyond just theory to observed phenomenon. British coal output, which peaked in 1913, is a classic Hubbert formation.