So what if oil prices have just set yet another record? They have been soaring for years without stunting global economic growth, profits or share prices, and without stoking high inflation, the curse of past oil crises.

So far so good, but for how long? As oil topped $75 a barrel, some economists began to ask again if the latest spurt in a four-year rally will push costs beyond tolerance levels, sparking inflation in earnest or a drop in business activity as companies buckle under bills.

Andrew Oswald, Professor of Economics at Britain's Warwick University. "The resilience of Western economies to recent oil shocks has been remarkable. But presumably it cannot last."

Neither Mr Oswald nor any of the other experts on oil economics knows for sure what is waiting round the corner, and experience from previous decades may be a poor guide.

Oil prices have more or less doubled in the past two years and more or less tripled since 2002. Yet, global economic growth hit its fastest rate in 30 years in 2004, at 5.1 per cent, despite a 30 per cent jump in the price of a barrel of Brent in that year alone.

That's a far cry from the recessions that followed the crises caused by the Arab oil embargo of the mid-1970s and the Iranian Islamic Revolution in 1979 followed by the 1980-1988 Iran-Iraq war.

GDP growth remained above its long-term average last year at 4.3 per cent when oil prices rose yet another 30 per cent and is forecast to do just as well if not better this year. And there has been no sign of any major surge in inflation.

The International Monetary Fund has saidthat previous crises cut US GDP by half of a per centage point on average and pushed inflation upwards by about three-quarters of a point, but that this time round the effect was not as marked, due to better monetary policy and lower interest rates.

James Hamilton, Professor of Economics at the University of California, San Diego, has spent much of his career documenting the ups and downs of an oil-driven economy, and he is sanguine about the latest rally in crude prices.

"Overall, the world economy weathered the 2005 oil price increases with less economic damage than I had been anticipating," he said. "That leads me to believe that $70 oil is not, by itself, a cause for major alarm at this time."

He argued, until recently at least, that the oil crises of the past were different and more damaging because the oil price rises were more abrupt and, above all, because they were about producer countries turning off the oil taps.

According to that argument, what crisis there is nowadays is more of a "demand crisis" - caused by the breakneck pace of economic expansion in countries such as China, now the world's second biggest consumer of oil after the US.

That theory, which assumes a demand crisis was more benign than a supply crisis, looks increasingly tenuous since attacks by militants halted a substantial part of Nigeria's oil output, and above all the current standoff over the nuclear intentions of Iran, the world's fourth largest producer.

Eric Chaney, chief European economic at US investment bank Morgan Stanley, said cheap Chinese exports and labour have put a lid on global inflation worldwide in recent years, but that the current threats to oil supply combined with tighter monetary policy amounts to a potentially toxic mix.

Mr Chaney said: "I'm worried because factors that have pushed crude prices above $50 and now $70 are more and more supply-side events or worries (Iran, Nigeria, lack of refineries).

"I'm afraid that inflation expectations may take off and that Europe may experience a double whammy: a higher oil bill and higher nominal rates."

The Organisation of the Petroleum Exporting Countries (OPEC) also noted the risk to households of higher fuel bills at a time when they are also facing higher credit costs because central banks are pushing up interest rates to keep inflation at bay.

"Sustained higher energy prices may pose a risk to growth, especially in economies where consumer budgets face pressure from rising interest rates," OPEC said in a monthly report.

For Adam Posen of the Institute for International Economics, the risk to households is bigger in the United States because there is less public transport and more long-distance driving, and the risk is proportionately greater for poorer homes.

"This is bad, but it will have little effect on overall growth or inflation forecasts," he said.

French Finance Minister Thierry Breton, mindful of how easy it is to lose voters because of high petrol prices, says that he will raise the issue this weekend at talks in Washington among the leading industrialised powers.

But he, and they, have done so before - to little avail.

For business and investors, the principal question is how much longer can firms continue to bear rising costs for energy and other commodities. They have done well so far seemingly.

Indeed, last year alone, profits made by companies quoted on the main blue-chip indices of countries such as Germany and the US rose more than 30 per cent despite the surges in energy costs. The year before was even better in many places.

In Europe, economists believe companies absorbed much of the pain by keeping wages down and shedding staff, avoiding the need to raise the price of their goods and risk losing market share.

That brings the economists, politicians and everybody else back to the initial question - for how long?