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- The rapid drawdown of the U.S. Strategic Petroleum Reserve could damage the caverns that store the oil, experts warn.
- The SPR has tumbled below 300 million barrels for the first time since it was filled in the early 1980s, according to federal data released this week.
- The SPR faces elevated risks to its operations and cavern integrity as inventories continue to drop.
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The caverns that hold the U.S. strategic oil reserves could get damaged by the rapid release of stockpiles in response to the Iran war, experts warned this week as inventories hit a four-decade low.
Damage to the caverns would make it more difficult to respond to future energy emergencies, the experts said. The oil in the Strategic Petroleum Reserve (SPR) is stored at 60 salt caverns thousands of feet underground at four major sites along the Gulf Coast in Louisiana and Texas.
The SPR has tumbled below 300 million barrels for the first time since it was filled in the early 1980s, according to Department of Energy data released Monday. Inventories are depleting as the U.S. releases 172 million barrels in response to the supply disruption caused by the Iran war. The SPR will sit at around 243 million barrels after the drawdown is finished.
The Energy Department has said at least 70 million barrels must remain in the reserve to safely manage the caverns. Amos Hochstein, a senior energy advisor to President Joe Biden, disputed that figure this week.
“Don’t believe the people out of the government that are saying the SPR can go to 70 million barrels. It’s nonsense,” Hochstein told CNBC’s “Squawk Box” Thursday. At that level, the reserve would be depleted to “the point of never resurrecting it,” he said.
Depleting the reserve below 300 million barrels risks damage to the caverns, the former Biden administration official warned in June.
“I don’t know anyone who believes we can go below 300,” Hochstein told CNBC’s Brian Sullivan at an Atlantic Council event. “I know plenty of people who think we can’t get near 300 because physically you will damage the caverns where the oil is stored.”
Energy Department spokesman Ben Dietderich said claims that the SPR’s storage caverns are at risk of collapse as oil is drawn down are false.
“The caverns are always full. All that changes is the ratio of oil and water that is filling them,” Dietderich told CNBC in a statement. The Trump administration is “responsibly managing the SPR as the critical national security asset it was designed to be,” he said.
Both sides of the political aisle have voiced worries about the integrity of the salt caverns. Republican lawmakers raised those concerns when the Biden administration released a record 180 million barrels in response to Russia’s invasion of Ukraine in 2022. The SPR fell below 350 million barrels in 2023 under Biden. It was refilled to around 415 million barrels before the Iran war.
The Strategic Petroleum Reserve Bryan Mound storage facility located in Brazoria County, Texas, is one of four sites that make up the country’s oil reserve.Str New | Reuters
The Government Accountability Office said in a May report that “repeated partial drawdowns followed by refill can leach a single part of a cavern repeatedly, leading to undesirable shapes.”
The majority of the SPR’s caverns were found to be in “very good condition” after the 2022 drawdown, according to the GAO.
“However, every drawdown cycle expands cavern volume and reduces the spacing between caverns within the salt dome, which ultimately reduces their long-term viability,” it said.
Operational floor
To release oil from the SPR, operators pump water into the bottom of the caverns to displace the crude to the surface and pump it through wells into pipelines.
Seventy million barrels is the strict physical minimum needed at the top of the caverns to keep the extraction pipes safely submerged in oil rather than water, said Siddharth Misra, a petroleum engineering professor at Texas A&M University.
But “the practical operational floor for the crude inventory is between 250 million and 300 million barrels,” Misra said in an email to CNBC. At current inventory levels, “cavern integrity and overall operational capability are at an elevated risk,” he said.
When the inventory drops below 300 million barrels, the SPR loses its ability to pump oil at rapid speeds to address emergencies, Misra said. The system’s pipes and pumps could also get damaged as the oil layer thins at the top and sludge rises toward the extraction intake at the cavern ceiling, he said.
Fresh water is often pumped into the caverns during rapid drawdowns, which dissolves the salt walls, Misra said. This “creates flatter, less stable roof and severely thins the critical salt pillars that separate adjacent caverns, greatly increasing the geological risk of a structural cave-in,” he said.
The SPR was originally designed for five full drawdowns. Instead, it has executed dozens of large and small releases over the past 40 years, Misra said.
“Because the system was not designed for this many cycles, the repeated injection of water and extraction of oil have caused severe cavern deformation, accelerated the rate of massive salt falls from the ceilings, and significantly weakened the overall structural integrity of the aging reserve,” he said.
Energy Department officials told the GAO that they are “holding the SPR infrastructure together with ‘Band-Aids,’ and that it is uncertain how long they will hold.” More than a quarter of the SPR inventory was “not available for drawdown due to a combination of construction outages and cavern outages” as of December 2025, the GAO found.
Analysts at Rapidan Energy, for their part, estimated the SPR has a “soft-ish floor” of around 170 million barrels, below which “cavern integrity and pumping infrastructure limitations argue against further draws.
Hochstein said a hurricane in Florida or Louisiana could put the U.S. in a tough position at current SPR levels. “Below 300 million, which is where we are now, it is not that we can’t do it, but it slows the flow and puts us in danger,” he said.
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