Petrol and diesel prices have surged to a six-month high, fuelled by mounting tensions in the Middle East.

Pump prices rose 2.5 per cent over the past four weeks as fear of war in the Gulf sent the cost of oil spiralling upwards.

Petrol now averages at 92 cent per litre and diesel at 84.8 cent per litre, aAutomobile Association (AA) survey reveals.

"It's a sharp rise in the space of a month so it is certainly unwelcome; but it is not a surprise given the recent rise in oil prices," said AA public affairs manager Mr Conor Faughnan.

The relative strength of the euro has cushioned motorists to date, the AA said.

"We have been spared even more severe rises recently because of the euro's rise against the dollar. But with oil prices internationally reaching $37 per barrel, the outlook would appear to be poor for now," Mr Faughnan added.

Uncertainty in world markets is likely to prompt further price increases over coming weeks, the AA warned.

But amid deepening political volatility in the Middle East, it is difficult to predict if pump prices will continue to escalate over the longer term.

Prices varied significantly between retailers, the AA found. "We have found garages selling unleaded petrol for as little as 84 cent or as much as 99 cent," said Mr Faughnan. "The pattern is much the same for diesel. This is an enormous range."

Motorists were urged to use their discretion and shop around for the best value. The Consumers Association (CAI) said drivers should pay greater attention to price-per-litre rather than purchasing petrol in €10 or €20 increments.

"The consumer must be prepared to become more price sensitive. At the very least, he or she should make note of how much they are paying," said CAI chief executive Mr Dermott Jewell.

"It has been shown that prices can vary by as much as 12 cents per litre between outlets. There is no excuse for this variation but it is up to the consumer to challenge it by avoiding paying over the odds."