Opinion: The recent hike in energy prices was not caused by OPEC countries holding back oil supplies. Neither was it the result of oil companies failing to invest in the right type of refinery. Instead, I believe that we are facing a far bigger problem with oil supply whereby geological constraints rather than short-term market considerations will dictate the agenda.

I believe that, before this decade is out, we will see a peak in global oil production and that, once we cross that threshold, we will start to see prices rising dramatically as the inelastic demand for oil will have to cope with steadily dwindling supplies. We will look back on the cheap days of oil at $50 a barrel and realise that the recent blip in prices was just the first scared reaction from oil traders when they sensed the possibility of shortages to come.

In his article last week, energy journalist John Walsh argued that increased investment in complex refineries to handle the glut of heavy Saudi oils now on the market would help solve our immediate problems.

These sulphur-laden oils sell at up to $11 a barrel discount on the more publicly traded light crude oils. This is because the light oils are more suitable for refining into transport fuels. The real question is why Saudi Arabia (the last great hope for those who think a peak in oil production is still a generation away) cannot find additional supplies of these lighter oils that the market clearly wants.

The International Energy Agency (IEA) issued its World Energy Outlook 2004 last week - which no doubt provided some reassurance for those who think business will continue as usual.

Its analysis was that oil supplies were unlikely to peak before 2030 but it was notable that, for the first time, it was putting a number of caveats on that prediction.

Whereas a similar report in 2002 had spoken of "ample" energy supplies, the agency director is now clearly warning that our continuing heavy reliance on fossil fuels is "deeply disturbing".

The report also acknowledges that the reliability of oil reserve data has been called into serious question, and calls for a new transparent, comprehensive and consistent system of reporting of reserves.

One person who has carried out such a field-by-field analysis is a former oil company geologist Mr Colin Campbell who lives in west Cork and who has set up the Association for the Study of Peak Oil (ASPO).

He shows how a peak in discoveries of oil occurred in 1964 and argues that we are now only left with the deepwater, polar, and sand and shale oil deposits to discover - all of which are very energy-intensive and expensive to exploit.

His most optimistic estimate is that global production of conventional oils will peak in 2008 and will decline by over 2 per cent annually after that. And, unlike the oil companies and national governments, he has nothing to gain from the way in which the story of future oil supplies is told.

His predictions have been backed up by the work of Chris Skrebowski, editor of Petroleum Review at the Energy Institute in the UK, who has charted all the mega oil fields (ones that can produce over 100,000 barrels of oil a day) which will come on stream over the next six years.

His analysis shows how there will be significant new supplies coming on the market for the next three years but, after that, we will be down to only three new mega fields a year.

We will not have the supplies to cover the depletions from older fields (which are already reducing by one million barrels a day each year) nor will we have the necessary supplies to meet the annual increase in market demand.

As long as no terrorists get their hands on some vital pipelines, I would expect the market price of oil to drop back from its current highs - as has started to happen.

However, by the end of the decade, I believe price-rises will go a lot higher than the 2.5 per cent per annum increases predicted by the experts quoted in Mr Walsh's article last week.

It all depends on the quantity of oil reserves that the Middle East actually has.

And the real question is whether the expected level of reserves - like the weapons of mass destruction - proves to be there.

Mr Matt Simmons is head of Simmons & Co, a leading energy investment bank, and energy advisor to George Bush. Mr Simmons has recently predicted that the largest Saudi fields may be much closer to depletion than is commonly expected.

He is concerned that the 40-year-old Ghawar field, which provides five million barrels a day (over half of Saudi production), may deplete much more quickly than expected due to the intensive water-pumping techniques that have been used to keep the reservoir pressure up over its lifetime.

Moreover, the IEA World Outlook estimated that over $100 billion (€78 billion) would have to be invested each year on production, distribution and refinery infrastructure to get the necessary supplies out of the OPEC countries.

Finally, we should listen to the president of OPEC, Mr Purnomo Yusgiantoroof, who said this summer that oil prices were at crazy levels, but that OPEC was powerless to cool the market given that "there is no more supply".

We will only know exactly when oil peak has happened several years after the event - but we certainly need to start planning for it now.

Eamon Ryan TD is Green Party Energy spokesperson. The Green Party will be hosting a public debate on peak oil on Monday, November 29th