The Hubbert Curve

The Hubbert Curve is not a chart of an individual field's production but rather a mathematical statistic formed from total output of many fields. This page looks at the basic principles behind it.

M King Hubbert (1903-1989)

An individual field's production generally appears something like H1 - a gradual increase to maximum output, then a long plateau and a gradual decrease.

H1. Individual Well Production

When you combine many fields together, placing a small number of large fields near the beginning and a large number of small fields at the end, as happens in oil exploration, the combined values produce something like a bell curve. The examples below (H2 and H3) show how just four and eight 'wells' begin to approximate the shape of the Hubbert Curve.

Obviously the more wells you add, the smoother the curve. The US-48 had around 240,000 producing wells in 2002 (ASPO).

It must be remembered that the Hubbert Curve is a theoretical curve that is only likely to occur in long and stable areas (such as the US-48). Most curves are distorted by wars, recessions, political interference, etc, and are rarely symmetrical. But the most important principle of the Hubbert Curve is not the shape but that fact that when approximately half of the total oil is extracted, production will inevitably decline.

The Example of the US-48

The most outstanding example of the Hubbert Curve predicting future oil production was the initial forecast of the US-48 (which excludes Alaska and Hawaii) by Hubbert himself in 1956.

Earlier predictions had simply divided the known reserves by production (the R/P ratio) and they failed because they had not taken into account future discoveries. M King Hubbert (1903-1989) was an American geophysicist who realised that it was not when oil ran out that mattered but when it began to decline. He made two educated guesses for how much oil would be discovered and produced – 150 and 200 Gb (ASPO's latest estimate is 195 GB). After making plausible estimates of future production rates for both guesses, he came up with the early 1970s for the more optimistic. The actual peak year was 1970.

The curve for the US-48 (which can be seen in D2) shows several features. There is no noticeable effect from major wars such as the Second World War (1939-45) and the Vietnam War (1957-75). There was also a slight increase in production in the early 1980s but that did not last long or change the general trend. The US-48 curve shows that events such as wars, recessions and oil prices do not dramatically effect production (unlike consumption) unless they actually concern the oil wells. If the Second World War had actually effected the US region itself, with air attacks or invasions, oil production would also have been effected.

The clear proof of how the large oil wells are found first and the end of the downslope results in many small wells is shown by comparing the producing wells of the USA and Saudi Arabia (source: ASPO 2002).

Applying the Curve to the World

The example of the US-48 shows a fine example of the Hubbert Curve in action. But other countries have examples which are not so neat. Iran's curve P6 shows a double peak and the world so far (right) looks more like the Himalayas. At the moment, the world seems to be bumping along at the peak P5 but could this be the first of two or more? Could the world production have another peak later on like Iran's?

The cause of both these effects are known. In Iran, there were wars and revolutions which effected oil production. As we saw in the US-48, external wars and revolutions do not alter production unless they bear on the wells themselves. In Iran they did which is why there was a gap in the curve and a second peak. As far as the world is concerned, if there had been wars which effected the oil wells on the curve up (which would have meant the USA, the North Sea, Saudi Arabia, etc) there would have been a drop in production and a double curve. The drop in the curve in the 1980s was due to recession which reduced demand, therefore lowering production (through choice). When the peak occurs, production will fall through necessity – countries will not be able to raise production whether they want to or not.

The example of world discovery also suggests that there is no more oil waiting to be brought online for a second peak. Even if it was discovered today, the time lag would not bring it online for a decade or so.

War may well effect oil production in the future. We have already seen several wars in the Middle East over oil; that is likely to occur again and again as supplies shorten. Since they will actively effect the wells, production is likely to drop then, so adjusting the Curve. But these will be valleys and peaks on the downslope. If you imagine the upslope curve of the world above reversed, the valley might be where a war was fought in Saudi Arabia. Once the war was finished, a small peak would follow as production began again, but that peak would not be higher than the main peak, the peak of highest production. World oil production seems to be peaking now. There is no reason to assume that oil production will rise higher in the future.

Mathematics

A mathematical explanation of the Hubbert Curve by Luís de Sousa can be read on this page.