New York's main contract, West Texas Intermediate (WTI) for February delivery, was up one cent at $91.81 in mid-morning trade, while Brent North Sea crude for February eased seven cents at $106.68.
Under the deal initially reached in November, iran agreed to curb parts of its nuclear drive for six months in exchange for receiving modest relief from international sanctions and a promise by the so-called P5+1 -- Britain, China, France, Russia, the United States plus Germany -- not to impose new sanctions against its hard-hit economy.
This will give both sides time to come up with a more comprehensive solution to the dispute.
Tehran has been subject to painful international sanctions aimed at bringing to an end its nuclear programme, which the West claims is being used to develop atomic weapons. iran vehemently denies the claims.
The Islamic republic, a member of the OPEC cartel, pumped 2.8 million barrels of crude in December, according to data from the US Energy Information Administration (EIA).
"Investors are quite aware that prices will come under pressure if iranian oil eventually returns to the market, but they also know that it will take a while for production to return," David Lennox, resource analyst at Fat Prophets in Sydney, told AFP.
Lennox said dealers were also keenly awaiting the latest official US stockpiles data to be released Wednesday for clues about demand in the world's biggest oil consumer amidst a record-breaking North American cold snap.
"The extreme weather in the United States not only affects demand but has caused several supply disruptions as well," Lennox said.
AFP reports from SINGAPORE