The impact on the tanker trade remains unclear as oil buyers could turn to regular sources such as Saudi Arabia for more barrels, or look further afield at long distance sources such as the US.
Iran will use various methods to prevent a possible reduction in its oil exports after re-imposition of the USA sanctions.
The United States exited from the nuclear deal between Iran and world powers in May and said it would reimpose economic sanctions on the Islamic republic and its business partners by November 4.
London Brent crude fell 55 cents, or 0.7 percent, to $78.68, after gaining more than 5 percent last week.
Three members of the Organization of Petroleum Exporting Countries - Libya, Iran and Venezuela - are posting real, or have expected, production declines. West Texas Intermediate, the USA benchmark for the price of oil, was up 1.51 percent to $75.06 per barrel, its highest level since November 2014. "Iran. OK. You think of it. Iran is their big enemy, so they are going to have to do it", Trump said. "We are also working with oil market participants, including producers and consumers, to ensure market stability".
Merkel gives in: German chancellor agrees to tighten immigration policies
German politicians who criticized the agreement say Merkel and her conservatives had abandoned the country's moral mission. The most important factor for her survival is probably how long her own CDU lawmakers stand by her, and for now they are.
"OPEC is manipulating, and you know they allowed (a production increase) less than we thought last week".
Trump was not specific on whether the additional 2 million barrels was a per-day figure - but worldwide daily demand is nearing 100 million bpd.
They agreed to bring down overcompliance with the cuts, resulting in an output increase of one million barrels a day, according to the Saudi energy ministry.
Saudi Arabia, which has been pumping around 10 million barrels per day, holds the largest spare capacity in the world and is the only country that can add substantial supply to the market.
Trump will visit Europe this month for a meeting with North Atlantic Treaty Organisation allies, whom he has criticized sharply as paying too little for their joint defense.
European countries have been attempting to negotiate exemptions for their firms, but the official confirmed that US President Donald Trump intends to stick to his deadline.