Long-dated oil prices have risen to within a whisker of $100 a barrel, in a sign that investors are expecting high prices to return after the recession.

The furthest forward oil contract traded on exchanges – the December 2017 futures – rose last week to $99.97 a barrel for the Brent benchmark and to $99.43 for the West Texas Intermediate, the highest since last October. The prices have risen by 10 per cent in the last month.

“The entire crude forward curve has moved up,” said Michael Wittner, oil strategist at Société Générale. “We assume that investor flows have pushed up long-dated prices.”

Long-dated oil prices are now almost $20 a barrel higher than two years ago, even though spot prices are much lower than then. Spot prices oil ended last week at $77.65.

The International Energy Agency, the rich countries' watchdog, has admitted for the first time that the spike in prices last year played a significant role in tipping the world economy into recession.

An unauthorised draft of the World Energy Outlook, the agency's flagship report, says that high prices made oil- importing countries more vulnerable to the recession by damaging their trade balances, reducing household disposable income, dampening growth, and putting upward pressure on inflation and interest rates.

“The run-up in oil prices in the period 2003 to mid-2008 arguably played an important, albeit secondary, role,” the draft report states, adding that a renewed run-up in prices as the still-vulnerable economies were beginning their recovery would have a similar destabilising effect.

Oil traders, companies' executives and analysts are split over the reasons for the rapid rise in long-dated prices.

Some say the rise reflects long-term oil supply worries, despite the impact of recession on global demand. Others say that with supply outpacing anaemic consumption, traders need the incentive of higher forward prices to store petroleum the world does not need.