The threat of rising production costs has been heightened after oil prices climbed to nearly $80 a barrel – the highest level for five weeks.
During post-Christmas trading in London, US crude touched $79.12 a barrel before falling back later to $78.77.
Heating oil futures led the gains, while London Brent crude rose by more than a dollar to $77.32 a barrel.
Prices rose following forecasts of colder weather in the United States, and the expectation of increased consumption and falling reserves.
That would indicate that demand was rising and signal an improvement in the US economy.
Oil analyst Christophe Barret at Calyon said ongoing political problems with Iran threatened to keep oil prices high.
He said: “Remember how prices went up recently when soldiers from Iran went into Iraq and occupied an oilfield.”