Oil prices slipped back below $145 US a barrel Friday as the U.S. dollar strengthened slightly against the euro and the Japanese yen.

Suggestions by Saudi Arabia's oil minister that the world's biggest oil exporter doesn't plan to boost production had helped bolster prices earlier in the session.

Trading volumes were lower than usual as U.S. markets were closed for the July 4 holiday.

Light sweet crude for August delivery was down $1.20 at $144.09 US a barrel in electronic trading on the New York Mercantile Exchange.

Crude futures rose to an intraday record of $145.85 US in New York on Thursday before settling at a record finish of $145.29 US a barrel — up more than 50 per cent so far this year.

Saudi Arabian Oil Minister Ali Naimi said Thursday that he had no immediate plans to boost crude output unless supply-and-demand fundamentals have changed. But for now, he said, "all our buyers are satisfied and happy."

Gains by the U.S. dollar against the euro helped keep oil prices from rising further. The greenback strengthened after the European Central Bank raised its benchmark interest rate an expected quarter-point Thursday but signalled it didn't expect additional rate hikes that might further boost the euro.

On Friday, the U.S. dollar was stronger against the euro at $1.5694 US. It also gained to 106.81 Japanese yen.

A falling dollar has helped boost U.S.-dollar-denominated oil prices, an effect augmented by investor purchases of commodities as a hedge against inflation and an alternative to dropping stock markets.

Sabre-rattling in the Middle East is another reason for high oil prices, with traders particularly concerned that a conflict with Iran could disrupt tight global supplies.