ONE day, oil production will begin declining. The world's drivers and transport operators and airlines, not to mention fertiliser, plastics and pharmaceutical manufacturers, will file their usual orders - only to be met by suppliers saying: "Um, sorry, we can only meet part of that order."

Imagine the panic. Imagine the shock to markets. And imagine if that moment were to come not in 2130, or even 2030, but in 2013?

The economic uncertainty would eclipse the current recession, the potential for global conflict would shoot upwards, and some predict that we'd face the dark prospect of global oil apartheid, where rich countries might corner supplies - and poor countries would be left lurching, their very survival as states possibly at risk.

For years, those who have raised the spectre of "peak oil" have been derided as cranks and alarmists. But their ranks now include some remarkably conventional figures, and the statistics they use have the most respectable origins.

Often misunderstood, "peak oil" does not refer to oil running out. That won't happen for a long time. Peak oil simply refers to the time at which overall production peaks and, most likely, demand begins to outstrip supply.

The world consumes 85-million barrels per day. The International Energy Agency (IEA) expects demand to hit 105-million barrels per day by 2030. But it's not clear how this 20-million barrel-per-day gap will be filled.

Some extremely influential figures doubt it can be: the head of Total Oil, Christophe de Margerie, doesn't see global oil production ever exceeding 89-million barrels per day.

Ever since 1965, oil discoveries have been declining. While new, unconventional sources of oil, such as the Canadian tar sands, are coming online, they are costly to develop, and demand far more energy to mine, so the net energy return on investment declines.

Peak oil warnings started gaining worrisome credibility when, in November 2008, the IEA sharply revised its projection for the annual rate of decline of output from existing oil fields, from 3,7% to 6,7%.

The IEA describes itself as energy policy adviser to the 28 countries of the Organisation for Economic Co-operation and Development, which includes most of the Group of Eight countries, including the US.

Soon after, Fatih Birol, the IEA's chief economist, told British environmental journalist George Monbiot that global conventional oil supply "will come around 2020 to a plateau as well, which is, of course, not good news from a global-oil-supply point of view".

What's more, Birol's estimate depended, he said, on "timely" investment from the Organisation of Petroleum Exporting Countries (Opec).

Without Opec investment, that plateau would come sooner.

In 2008, several leading UK companies formed an industry task force on peak oil and energy security.

The task force includes major companies such as Virgin, Yahoo , Arup, Stagecoach and Solarcentury.

It released its first report in October 2008, warning that a "peak in cheap, easily available oil production is likely to hit by 2013".

Simon Taylor is one of the founding directors of the London-based nongovernmental organisation, Global Witness, which reports on conflicts over natural resources.

"If you took pre-recession projected demand, say from June 2008, when the oil price was at its highest, you could see demand going up in this quite steep curve, and if you plot what's coming on stream in next five, six or seven years, less the decline rate, you end up with a collision between the supply and demand curves somewhere around 2011," he says.

"If you do the same exercise with another project or two added (but bear in mind some have now been cancelled), and now with demand projected from around February 2009, then the lines collide later, around 2014."

"And if you project demand from this November, then the curve comes way back towards us again, somewhere around 2013. The collision point is somewhere around 2011-2014. Depending on how fast the economy recovers or not, and depending on possible moves to accelerate development of renewables, we have a real problem."

Where some see enormous risk, and where many choose outright denial, more imaginative business people see not only risk, but opportunity.

Will Whitehorn is president of Virgin's space business, Virgin Galactic, and is often described as Richard Branson's right-hand man. He chairs the UK industry task force.

Alarming as the peak-in-2013 conclusion may sound, he believes it is in fact a cautious report: "I think that we've taken a fairly conservative view of what the issue is here and I think we have a clear window of five to seven years to really make some fundamental changes to the way we use energy in the UK in order that peak oil does not become a crunch.

"We're not involved in this task force because of the implications for Virgin particularly, although obviously if you're one of the world's largest transport groups there are implications," he says.

"Because we've been believers that the possibility of peak oil is real, we've been investing in diversifying our businesses. That's why we've become one of the UK's largest long-distance train operators.

"We've also been investing in new aircraft types, which are more efficient and we're looking at issues such as carbon composites. In fact that's what our space launch system, which I've just unveiled in America, is made from. It's significant that three of the UK's largest transport groups are in the peak-oil task force, along with a big energy distributor and supplier. We face a risk, but we're getting ready for it.

"But the point about this task force is not about the risk we face. It's about the risk the people of the country and the government faces. And the fact that they're not getting ready for it. We're trying to persuade the government that this is a true and clear and present danger. The UK is no longer as energy self-sufficient as it was.

Whitehorn is clearly trying not to paint governments as blind and obdurate. "I do see government starting to take oil-supply warnings seriously," he says. "We're not a group that believes we're running out of oil. We're a group that believes the price of oil is going to become permanently high within a decade as cheap sources of oil cease to exist.

"We've got to be ready for a world with permanent 100-a-barrel oil. Oil is going to become too precious just to burn in cars. Oil is the source of our fertiliser, of our pesticides and pharmaceuticals, of most of our furnishings. It is the lifeblood of civilisation."

Right now, he says, "the first priority for national economies is energy saving.. Efficiency should become the watchword."

Nor does he wish to alienate any part of the energy sector: "I believe that there is a nuclear solution, there is a solar solution, a wind solution, a tidal power solution, a hydro solution.

"Anyone who lobbies one of those as being better than the others is very biased. The combination of them with much better energy efficiency should see us through this period of transition from an oil-based economy to a much broader source of energy supply."

The UK task force will release an updated report this month.

But, in the meantime, are governments starting to listen?

"I think the British government has been advised by its public servants that peak oil is not so much of an issue, because their understanding of what 'peak oil' means is based on the alarmism of the 1970s," says Whitehorn.

"The problem is quite a lot of public servants 'cried wolf' about this in the past . but eventually the wolf usually does come to the door.

"I'm not a doom-and-gloom merchant, I'm for doing things. If we can build a carbon-composite spaceship that is a 1000 times more efficient than current ground-based rocketry, I think we can solve the problem of peak oil."

n Le Page is a freelance writer.

'Some predict that we'd face the prospect of global oil apartheid, where rich countries may corner supplies - and poor countries would be left lurching'