Oil companies say they have little control over the prospect of huge petrol price rises in the coming months.
It comes as the strike in Venezuela and tension over Iraq pushed the cost of oil close to two-year highs. Esso has already raised the price of forecourt petrol this week.
Mr Howard Forti, manager of external affairs at Esso, said: "We had an increase this week of between one and two pence a litre.
"There are many factors that contribute to the changes in the price of a barrel and obviously commentators are linking it to what's happening in Venezuela and to the uncertainty in the Middle East.
"What's going on out there in the big wide world, those are factors that effect the prices of crude oil and when the price of crude oil is affected then people who are retailing petroleum based products obviously get affected. "There's nothing anyone can do about it."
City experts say oil companies and supermarket chains may have to charge up to 4p per litre more at the pump in the spring after a dramatic fall in oil supplies from Venezuela.
And military action in Iraq could fuel a further 5p per litre hike if the impact of any allied attack disrupts output from neighbouring states Saudi Arabia and Kuwait.
Responding to these reports, a Shell spokesman said: "It is possible that if there is movement in the market we compete with we could move our prices, but the general impression at the moment is we are not planning any rises.
"Generally speaking supply and demand dictates market sentiment - if there's a restriction on supply you would expect there to be a rise in the crude price."
PA