Hubbert theory states that oil production from a field or a group of fields will rise gradually, reach a peak in production and subsequentely decline.
If you take that at face value it's correct.
Oil is a non-renewable resource and logic dictates that the volume of oil produced must lie under a production curve (of whatever shape) and that the amount of oil produced can never be greater than the volume under the curve.
What hubbert theory doesn't mention is that it's talking about the production curve taking ONLY current technology into account.
Let's repeat that so we get it. At any one point in time, the amount of technically recoverable oil is x% of the total oil in there. 100 years the total recoverable oil from a field was 10%. That means that 90% of the oil from those old fields is still down there and not recoverable with the technology they used 100 years ago.
The actual amount of oil sitting in the ground, however is much larger than that under a hubbert curve at any one point in time. Some Old fields, for example, as stated still have 90% of the oil still sitting in them.
If technology stood still then you could say that a hubbert curve with a steep production curve upwards, followed by a sharp drop was a definitively predictable model for future production.
In the REAL world, however, technology is ever changing and this leads to reserves being stated upwards as new technology allows us to grab an ever greater percentage share of oil in place thus pushing any putative peak off or else flattening out a peak from a bell curve into a grand piano curve instead.
The church of peak oil dogma, however, reckons that only a perfectly formed bell curve is possible and that the reason reserves have been continually stated upwards is in fact due to OPEC lying for political reasons rather than technology.
A recent example would be stating that Canada has 300 billion barrels of reserves whereas ten years ago it only had 80 billion barrels.
Actually here in Alberta we are sitting on over a trillion barrels of oil in the ground just waiting on technology to pull it out. The technology exists: nuclear reactors.
Move along here nothing to see folks...