Last year, analysts and traders speculated that the Organization of the Petroleum Exporting Countries could do little to lift depressed crude markets with U.S. shale pumping away.

But as The Journal’s Markets Newsletter noted on Wednesday, an opposing worry is now taking hold–that the global oil cartel might not be able to halt a runaway oil rally even as it moves to produce more crude.

Oil’s recent rally has been undeterred by the prospect of higher production. Prices have gained 11% since OPEC gathered Friday and agreed to raise output. On Wednesday, U.S. oil futures rose to their highest level since November 2014, settling at $72.76 a barrel.

The shift in sentiment stems from a drop-off in Venezuelan production and concerns that harsher-than-anticipated U.S. sanctions on Iran could curb the country’s oil exports and exacerbate supply disruptions.

“If the administration is going to take as hard a line on Iranian exports as their statements would suggest, consumers are going to pay higher prices at the pump, even if OPEC and other countries produce as much as they can,” said Jason Bordoff, director of Columbia University’s Center on Global Energy Policy.

OPEC has faced pressure to increase supply as oil prices have soared, but analysts say major producers like Saudi Arabia and Russia may not be able to fill the gap left by other exporters.

“Saudi Arabia can’t save you from an oil price spike if you sanction Iran,” said Bob McNally, president of Rapidan Energy Group, a consulting firm. “That’s what the market is telling you.”

Rising energy prices could eventually crimp growth for major oil-consuming nations like the U.S. For consumers, prices at the pump–which have already climbed to three-year highs this year–could be heading even higher.