As oil prices bounce around the $45 mark one of the main factors underpinning the price rise is the increasingly popular notion of oil ''depletion''.
This is the idea that certain countries' reserves of oil have fallen to such low levels that they can no longer produce at the volumes they once did.
British trade journal Petroleum Review has reviewed the 2003 Statistical Review of World Energy, put together by British Petroleum, to look for signs of depletion.
Its study claims that a large group of producer countries are now in decline - putting even more pressure on those countries who have spare production capacity.
There are several worrying aspects to this decline. The first is that added to the current increase in global demand, it means other countries must produce more just for the market to stay still.
Secondly, as those countries are forced to produce to their capacity, it only hastens the day when they too will have declining output.
Depletion speeding up
"What surprised me was the rate of decline among the 18 countries whose production is going down," Petroleum Review editor and oil analyst Chris Skrebowski told Aljazeera.
"The phenomenon of multiple counties all declining is a new one for everybody... So, in the longer term, matching demand to the new capacity of producer countries may prove to be a very tough call"
Petroleum Review editor
"For fourteen out of the eighteen countries the rate of depletion is speeding up. This has confounded a long held view that decline was a slow, gradual process.
"The first country to start to decline was the USA. It could be possible that because they have such a high skill base, so many wells and such cheap capital that they were able to slow their rate of depletion. Other countries cannot," he said.
Those 18 countries in decline amount to about 25% of the world's producers. They are losing about 1.14 million bpd.
This means that the other 75% have to increase output. Not only to add the extra barrels lost by the declining countries, but also to meet leaping global demand, about 2.4 million bpd in 2004.
That demand is set to continue its increase, forecast by the International Energy Agency to grow by another 1.8 million bpd in 2005.
"It's a crazy see-saw where the fulcrum, the pivot, is constantly moving across. Eventually it is going to get to a point where the see-saw can no longer balance," said Skrebowski.
Another problem analysts are facing is that it appears countries can carry on expanding production until suddenly the decline sets in, never to be reversed.
"The UK expanded production each year until 1999," Skrebowski continues. "Since then it has gone down every year by 5%, then 6% then 8% and this year, 2004, it looks set to be higher. This is even with the best technologies and techniques available."
Depletion could eventually make
current high prices seem cheap
The country with the biggest rate of decline is Gabon. The impoverished west African state experienced an 18% drop in production year on year.
This is on a set of fields who only came on the market in the 1970s, having been developed by the French oil companies. Such a rate of decline could spell disaster for vulnerable African economies.
Of course these are the most obvious examples of depletion. The more intangible effects are geo-political.
"Depletion is not very exciting or special if it is just in one country, say the west of country X is going down but the east is going up. No one really cares about that except those directly involved.
"If, however, it is going down in 'stable' country X and up in 'unstable' country Y, then you get the geo-political dimension. What happens if declines in safe countries can only be offset by increases from those less secure?" Skrebowski asks.
Because that is exactly what may be happening. For example Petrologistics, an oil industry firm which tracks tanker shipments, reported that Saudi Arabian output actually fell by 400,000 bpd last month.
No more room
"There are serious questions being raised about the ability of Saudi Arabia to expand production. Plus places like Abu Dhabi and Kuwait have little or no room for movement as well. And you don't need very many large producers to peak to make things very difficult for the others," said Skrebowski.
"It's a crazy see-saw where the fulcrum, the pivot, is constantly moving across. Eventually it is going to get to a point where the see-saw can no longer balance"
Skrebowski, on demand and supply
"As well as the 18 in decline there are many others who have no further room to expand production by any significant amount. Mexico has some problems with expanding any further and they do not appear to have invested in any new exploration whilst China's figures claim they are still just increasing capacity. Yet at the same time even they have admitted their two main fields are in decline."
Without gigantic and costly investment, that would itself inflate prices, squeezing more oil out of the ground may prove hard. Petroleum Review's rigorous statistical analysis may just be the prologue to a bigger, more unsettling story.
"The phenomenon of multiple counties all declining is a new one for everybody. Up to 1990 only the USA and Romania had started declining. So, in the longer term, matching demand to the new capacity of producer countries may prove to be a very tough call, a very tough call indeed," predicted Skrebowski.
And that may prove to be an understatement.