Brent crude futures were up 11 cents $78.35 a barrel.
Tehran blames rising prices on US sanctions imposed on Iran and Venezuela, founding members of the cartel.
Brent crude futures lost 85 United States cents to settle at US$77.39 a barrel.
The U.S. government plans to shut Iran's oil exports out of the market from November, demanding that all countries stop buying its oil.
"If Trump continues to believe that OPEC are not doing enough, we would not rule out a SPR (Strategic Petroleum Reserve) release from the USA, or possibly even export restrictions on petroleum products", ING said, in a note.
"Further declines in U.S. crude oil inventories and the significant outage in Libyan oil supply are helping to keep a floor under the market", said Harry Tchilinguirian, head of commodity markets strategy at BNP Paribas SA in London.
Iran's Oil Minister Bijan Zanganeh talks to journalists at the beginning of an OPEC meeting in Vienna, Austria, June 22, 2018. The contract added 20 cents on Tuesday, and there was no settlement Wednesday due to the United States holiday.
In his latest tweet on the subject on Wednesday, Trump said that the "OPEC Monopoly must remember that gas prices are up & they are doing little to help".
"This must be a two way street", he wrote, adding in block capitals, "REDUCE PRICING NOW!" Brent crude lost 38 cents to $77.84 a barrel.
Goldman Sachs said the market will stay in deficit in the second half of the year as actual and potential supply losses from Iran, Venezuela, Libya and Canada far exceed the proposed boost from Opec and its partners.
Oil prices dropped Thursday after weekly government data showed a surprise rise in USA crude stockpiles last week as refineries cut output, while gasoline stocks decreased and distillate fuel inventories rose.
After all the tough talk by the USA about countries cutting oil purchases from Iran to zero by November 4, India will have a chance to discuss the issue of crucial energy imports when a team of officials from the state and treasury departments visits the country this month.
USA tariffs on $34 billion in Chinese imports took effect as a deadline passed on Friday and Beijing has vowed to respond immediately in kind, setting the two world's biggest economies on a path towards a full-blown trade conflict.