For decades, the only answer to that question was the one first proposed back in 1956 by Marion King Hubbert, who argued that all oilfields hit a peak in production and therefore the world will also hit a peak and then decline.

But, try as he might the simple-minded Slug just cannot pin down a number which represents The Peak. In other words, while we debate the subject of oil production eventually hitting a peak, what is the magic number we're aiming for?

Think about that question, because it is rather important, and it leads to another question. How is it possible to debate Peak Oil, and the eventual decline of oil production, without first agreeing on the number which signifies the top, and the start of the decline?

True believers in the downside of Peak Oil cannot answer the question, preferring to slather their arguments in mathematical formulae and arguments which dodge the point - for a simple reason; they don't know.

Anyone who dares question the claims that the world is rapidly running out of oil is sent to the sin bin, or just ignored, because to question the logic behind Peak Oil is akin to heresy, much the same way that anyone who questions climate change is treated as nuts, or worse.

But, over the past three weeks as The Slug has been amusing himself with essays on the question of Peak Oil a few apparently overlooked points have been raised, such as:

• Why has the debate about a sharp decline in hydrocarbon production suddenly faded from the public agenda? (Slugcatcher, September 19)
• What happens to the price of oil and gas if Peak Oil has been postponed? (Slugcatcher, September 25)
• What number should we use for the peak? (today)

A series of events, and their related numbers, triggered this third and final instalment in the Peak Oil trilogy. All are linked to recent changes in the oil patch, including surprisingly optimistic assessments about how much oil is either being discovered thanks to new exploration and downhole extraction technologies or how much oil in old fields awaits the application of new techniques.

In the arena of discovery came a forecast from Harold Hamm, the Oklahoman behind the discovery and development of the Bakken oilfield, which spreads across the US states of Montana and North Dakota.

Officially, the Bakken contains up to five billion barrels of oil. That is the top number used by the US Geological Survey.

Hamm, who has used his exposure to the Bakken to lever his way into a $US7.5 billion fortune and ranking as the 36th richest man in the US, disagrees, substantially.

The view of the man who discovered the Bakken field is that it contains 24Bbbl of oil, close to five times what the academics at the USGS reckon.

The Slug might be old-fashioned but he reckons that Hamm has forgotten more about the Bakken than the USGS is yet to learn.

After Hamm came a report from Brazil that Petrobras, the government agency with the biggest foothold in that country's huge offshore oil discoveries under two kilometres of deep salt cover, reckons that it is sitting on 50Bbbl, much more than academics estimate.

Then there's one of the oldest fields of all, the Permian Basin of the US, which has already produced 30Bbbl but which is estimated by experts at Chevron to contain another 60Bbbl.

Until now, most of that residual oil in the Permian was regarded as unlikely to ever be extracted. Times are changing. A vast range of new technologies under the banner of enhanced recovery is unlocking the rest of the Permian, and while not all the oil will be extracted a lot more than previously imagined will be.

Do the maths: Bakken, 24Bbbl; Brazil, 50Bbbl; Permian 60Bbbl. The Slug knows that the total of 134 billion is a meaningless number because there are too many variables to say that even half the possible oil will be recovered.

But that misses the point. Those theoretical 134Bbbl are located in just three structures currently being subjected to greenfields drilling or new extraction technologies. Collectively they represent several years of total global oil consumption.

So, we return for a final attack on the Peak Oil argument.

Will someone please tell The Slug what the peak number is so he can watch out for the turning point in global oil output - or if that number is impossible to calculate, just as the Peak Oil argument is impossible to sustain when the oil price and new technologies are introduced into the equation.