How long does a century of oil actually last?

“The greatest shortcoming of the human race is our inability to understand the exponential function”, professor Albert Bartlett used to famously say. We tend to underestimate the impact of something growing at a steady rate, and nowhere is that more true than in the area of resource depletion. Because we don’t understand the effect of rising consumption, we are lulled into a false sense of security over how long supplies will last.

Mathematician Evar Nering explains:

Here’s the hypothetical situation: we have a 100 year supply of oil—that is, oil that would last 100 years if consumed at its current rate. But the oil is consumed at a rate that grows by 5% each year. How long will it last under these circumstances? It’s an easy calculation, about 36 years.

But let’s say we underestimated the supply, and we actually have a 1,000 year supply. At the same annual growth rate of 5%, how long will that last? The answer is about 79 years. Then let’s say we make a striking discovery of more oil—a bonanza—and now we have a 10,000 year supply. At the same rate of our growing use, how long would it last? Answer: 125 years.

How does this play out in the real world? We currently have 1.3 trillion barrels of proven oil reserves – enough to last 40 years. That’s proven reserves, so that’s only a fraction of what might really out there. This year production is expected to grow by around 1.5% this year and the next, and eventually drop down to 0.8% in the long term. It’s tempting to be blinded by the hugeness of the first number, and dismiss the smaller number as insignificant, but that would be a mistake. It’s especially important because the more we think we have, the more likelier we are to use more of it.

This mathematical reality seems to have escaped the politicians pushing to solve our energy problem by simply increasing supply. Building more power plants and drilling for more oil is exactly the wrong thing to do, because it will encourage more use. If we want to avoid dire consequences, we need to find the political will to reduce the growth in energy consumption to zero — or even begin to consume less.


  1. Consider this, the effect of -exponential- growth of human toil is still inferior to the -linear?-(is it not exponential in most of it’s curve!) growth of humanity, both brought into a proportional equation according to subject. (Leaving large margins as in human numbers coming to a standstill, or a temporary standstill)

    Relevancy urges to address human population as is, it’s growing numbers, and in the desire of how it could be of added value to planetary context, first and foremost. In parallel then, all the other issues, that are all dependent on this human numbers factor should be addressed knowingly that they are such: dependent.

    Exponentiality as in the multiplication of human numbers and human derivatives’ net worth, or rather net deficit, of course stands equally.

    Keep up the good work Jeremy,

  2. Update:

    To not sound like a machine, to simplify the suggestion: there is exponentiality in both: human numbers, and human resulting impact apart from direct presence.

    Now could there be exponentiality to be expected when the human combined curve of impact and numbers goes somewhere downwards? Especially as a consequence rather then an engineered effort to affect the planet?

  3. To put it mildly, one less human on the planet is of a larger impact of factors then reducing the footprint of one single person a 100 percent( a highly impossible feat). If we are to address exponentiality as well as other relevant concepts, say tipping points, loops, disruption, complimentation, and on, the greater exponentiality issue lies within human numbers.

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