Oil prices jumped more than 2 percent, hitting a four-year high, after the Organization of Petroleum Exporting Countries (OPEC) and other global producers declined to announce an immediate increase in production.
Benchmark Brent crude on September 24 hit its highest since November 2014 at $80.94 per barrel, before falling back to around $80.65.
The world's top oil producers, including OPEC members and non-members such as Russia, ruled out any immediate extra increase in output at a meeting over the weekend in Algeria, despite calls by U.S. President Donald Trump for action to raise global supply to help lower prices.
OPEC said in a statement that it was satisfied with "the current oil market outlook," citing what it said was "an overall healthy balance between supply and demand."
Trump withdrew the United States from the 2015 nuclear deal between Iran and world powers in May, and last month started reimposing sanctions on the Iranian economy that were lifted under the deal in exchange for curbs on Tehran's nuclear program.
A second round of penalties targeting Iran’s oil exports is due to come into effect in early November, and the U.S. administration has been pressuring other countries to cut their Iranian crude imports.
The market estimates that this will lead to a cut of at least 1.5 million barrels a day.
The website of Iran's Oil Ministry on September 24 quoted Oil Minister Bijan Zanganeh as saying that the "U.S. dream of getting Iran's oil exports [effectively] to zero won't come true."
However, Zanganeh acknowledged that South Korea, a U.S. ally, has not bought any Iranian oil "for three continuous months."
Even though several European countries have said they are seeking to protect their companies from renewed U.S. sanctions against Tehran, several major companies such as Total announced they were suspending activities in Iran.