Opec is concerned by the fall in the dollar and will take up the issue when it meets next week to chart supply policy.
A weaker dollar erodes income from the dollar-denominated oil sales of Opec members and could encourage them to seek a higher price. The currency is at a 20-month low against the euro.
"We are now concerned about the weak dollar," Qatari Oil Minister Abdullah al Attiyah said.
Opec is scheduled to meet on December 14th in Nigeria to assess the impact of the group's 1.2 million barrel per day cut, decided at an emergency meeting in October.
US crude was off 47 cents at $62.96 a barrel, holding last week's near-7 per cent gains, after earlier reaching a high of $63.82.
But Opec officials say prices could be higher still. "The price is firming somewhat, but against a weakening dollar, and there is still a lot of excess volume out there," Opec president Edmund Daukoru said.
In the past, Opec has said it needed higher oil prices to offset the impact of a falling dollar, but that was in late 2003 and early 2004 when US crude was trading in the $30s.