Looming strike action in major oil producer Nigeria was adding further support to prices, analysts said.
The price of reference light sweet crude for November delivery spiked at $53 a barrel in opening deals on the New York Mercantile Exchange on Thursday, the highest level in the contract's 21-year history.
US crude futures later eased to $52.30, a gain of 28 cents from the day's previous closing price.
In London, Brent North Sea crude oil for November delivery surged above $49 a barrel for the first time, hitting $49.20 a barrel in afternoon trading. It stood at $48.62 in late deals, a gain of 63 cents.
Prices continued their seemingly inexorable rise a day after the US Department of Energy reported a smaller-than-expected rise in US crude oil inventories and a fall in heating oil.
"If we do have a particularly harsh winter I think supplies could struggle"
UK energy analyst
Ongoing supply problems in the Gulf of Mexico were also causing concern.
"There's a lot of concern surrounding the levels of stocks in the US," said Veronica Smart, an analyst at the Energy Information Centre, a British-based consultancy.
"We're approaching winter when demand is obviously higher, particularly for gasoil. If we do have a particularly harsh winter I think supplies could struggle."
In the event of a cold snap, "we could definitely see Brent breaking $50 a barrel and heading further up," she predicted.