ALGIERS, Algeria—Saudi Arabia is running low on its most prized grade of crude, people familiar with the matter said, a development that could push oil prices higher.

After coming under pressure from the Trump administration over rising oil prices, Saudi Arabia is set to use an oil-producers’ summit in Algiers on Sunday to reassure oil markets that it can fill any shortages that arise as U.S. sanctions restricting Iranian oil sales begin in November.

But state-run oil giant Saudi Arabian Oil Co., known as Aramco, is telling potential buyers that its most highly prized crude will be in short supply in October after it underestimated the demand in advance of Iranian sanctions. And in the longer term, officials estimate Aramco wouldn’t have the capacity to meet future demand if Iran is no longer delivering oil, according to people familiar with the matter.

The scarcity could push prices above $80 a barrel, potentially putting a strain on U.S. consumers as they decide whether President Trump’s Republican Party will remain in control of both houses of Congress in November’s midterm elections.

With the combination of Iran sanctions and Saudi Arabia’s supply limitations, “we are heading to a price spike, likely $90 to $100” per barrel, one oil trader said. “It’s not just Iran that will suffer. It’s going to have a boomerang effect with rising gasoline prices” in the U.S.