Last year Trump made Saudi Arabia his first stop on his maiden global trip as a president. At the end of September, Trump reportedly called the Saudi King, and although the nature of that conversation was not disclosed, most oil watchers believed that the call was an attempt to pressure the Saudis into increasing oil supply.
Oil prices have risen in recent weeks ahead of USA sanctions on Iran - set to be imposed early next month.
Saudi Arabia welcomed Mr. Trump for his first overseas trip as president.
US President Donald Trump said Tuesday night that Saudi Arabia's king "might not be there for two weeks" without US military support, as he sought to pressure the close American ally over rising oil prices.
Trump continued the pressure campaign at a campaign rally in MS on Tuesday, where he offered some details about the conversation. "You have to pay for your military, you have to pay.'" Whether or not he actually said this to the King is questionable, but the fact that he appears to be insulting the Saudi monarchy in public offers more evidence that he wants them to lower oil prices from today's highs. However, analysts are warning prices could go up to $100 a barrel as the world's production is already stretched and Mr. Trump's sanctions on Iran's oil industry take effect in early November.
Mr. Trump didn't elaborate on when he made the comments to Saud Arabia's 82-year-old monarch.
Kazempour Ardebili, Iran's representative on OPEC's board of governors, said that US sanctions on Iranian oil were "impossible", and called on Trump to return to the nuclear deal with Tehran.
Oil prices are on the rise.
US crude inventories jumped 8 million barrels last week, quadruple analysts' expectations and the biggest build since March 2017, the Energy Information Administration said. The record high for Saudi output is 10.72 million bpd in November 2016. It was around $50 (€43) a year ago.
The call grabbed the attention of oil traders and hedge funds, who are watching closely for any signs that the USA might take action against Saudi Arabia or other members of OPEC after Trump used his address at the United Nations General Assembly in NY on September 25 to hammer home those views.
"They'll pay us. The problem is nobody ever asks".