Oil prices rose to five-month highs in Asian trade on Thursday after figures showed US crude reserves increasing at a lower-than-expected rate, analysts said.
New York's main futures contract, light sweet crude for delivery in June, gained six cents to 56.40 dollars a barrel.
Brent North Sea crude for June delivery was up 27 cents to 56.42 dollars.
The US Department of Energy's weekly inventory report on Wednesday showed a 600,000-barrel increase in crude stockpiles for the week ended May 1, far less than the two-million-barrel build-up, analysts expected.
The lower-than-expected increase was a sign of resurgent "oil demand optimism," said Phil Flynn of Alaron Trading.
"The reason why oil is rising is because of hopes that the economy can recover at a time when OPEC (the Organisation of the Petroleum Exporting Countries) is cutting back on production," he added.
Crude futures on Tuesday began hitting multi-month highs on hopes of a recovery in energy demand, alongside rising stock markets.
However, Mitsubishi Corp's risk manager Tony Nunan warned that pre-existing problems in the oil market remained unresolved, and might pose a challenge to existing prices.
"Overall, the fundamental picture still doesn't look good. The total inventory picture is still very high," said Nunan, who is based in Tokyo.