Pressure from Mr. Trump did help prod Saudi Arabia, Russia and other producers to agree to gradually increase supply by as much as 1 million barrels a day at meetings on June 22 and June 23 in Vienna. “We will do whatever is necessary to keep the market in balance,” the Saudi energy minister, Khalid Al-Falih, told journalists at OPEC headquarters in Vienna at the end of the meeting, with Russia’s energy minister Alexander Novak seated at his side.

Since then, though, the Trump administration has upped the ante by signaling a tough line on closing down Iranian production. Since the lifting of sanctions in 2016, Iran has returned as a major oil supplier, selling around 2.5 million barrels a day, or more than 2 percent of global supplies. Traders worry that a major curtailment of Tehran’s output could risk creating a supply crunch that might drive prices skyward.

“If we take 2 million barrels of oil off the market, what is going to be left in the tank?” Ms. Croft asked.

Mr. Trump said in his tweet that he had asked Saudi Arabia to increase production to compensate for what he called “turmoil & disfunction in Iran and Venezuela.” But most analysts think that coming up with that much oil quickly would be a challenge for the Saudis.

Saudi Arabia, for instance, says it has 2 million barrels a day in spare capacity, but analysts are skeptical that it can easily and sustainably add more than 700,000 barrels of production a day without drilling and other work that would take time. “Once you get above that level, we are into uncharted territory,” said David Fyfe, chief economist at the Gunvor Group, a major trading house. “Can they really push above that quickly?”