Strategic oil inventories have researched a 40-year low, and experts warn their continued depletion could damage the underground caverns where the reserves are stored.
Last week, the Strategic Petroleum Reserve (SPR) plunged below 300 million barrels for the first time since the 1980s, when the reserves were being filled, according to the Department of Energy. That pool is expected to drain further to 243 million barrels as the U.S. releases 172 million barrels to manage severe supply disruptions and rising energy costs due to the Iran war.
Those reserves are kept in 60 salt caverns across two sites in Texas and two sites in Louisiana, each thousands of feet underground and have a total storage capacity of 714 million barrels. But as oil is drained from these reserves, the integrity of the caverns may be imperiled.
“I don’t know anyone who believes we can go below 300,” Amos Hochstein, a senior energy advisor for former President Joe Biden, told CNBC on Saturday. “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.”
The Department of Energy denied Hochstein’s claim the changing inventory levels risk harming the caverns.
“The caverns are always full. All that changes is the ratio of oil and water that is filling them,” DOE chief spokesperson Ben Dietderich told Fortune in a statement. “President Trump and [Energy Secretary Chris Wright] are responsibly managing the SPR as the critical national security asset it was designed to be, helping stabilize oil markets and protect Americans from supply disruptions.”
The health of the caverns as political ammo
Both Republicans and Democrats have used the status of the caverns as political ammo on issues surrounding the SPR. In 2025, Wright testified to the House Energy and Commerce Subcommittee on Energy that President Donald Trump’s efforts to replenish the SPR were hampered by more than $100 million in necessary repairs to the reserve’s facilities. The restoration, he argued, was a result of the quick drawdown of reserves following the Biden administration selling nearly 200 million barrels in 2022 and 2023 to steady global energy costs amid Russian’s invasion of Ukraine.
“The immediate thing we need to do is finish the repairs on the Strategic Petroleum Reserve,” Wright said in testimony. “It was drawn down so quickly, and that causes some damage to the infrastructure itself. Those repairs are ongoing, and it costs a nontrivial amount of money to repair the SPR.”
As of May, most of the SPR’s caverns were in “very good condition” following the drawdowns, according to a report from the Government Accountability Office (GAO) released to the public in June. However, the GAO warned “every drawdown cycle expands cavern volume and reduces the spacing between caverns within the salt dome, which ultimately reduces their long-term viability.”
Concerns about the future health of the caverns
Engineering experts, indeed, still have concerns about the longevity of the caverns given the repeated drawdown of the SPR. Siddharth Misra, an associate professor of petroleum engineering and geophysics at Texas A&M University, explained that when the caverns were constructed in the 1970s and ‘80s, they were designed to have an initial 25-year lifespin, engineered to handle just five drawdowns and refills. Instead, the facilities have endured dozens of releases in that timeframe.
During these drawdowns, the total fluid volume inside the facilities must always remain at 714 million barrels, meaning operators must pump fresh water into the facilities to keep pressure stable, Misra noted. The water “aggressively dissolves the salt walls,” widening the cavern and thining the walls separating the adjacent chambers. Moreover, pumping so much cool water inside the caverns, which naturally have a higher temperature, can result in thermal shock, causing large pieces of salt to fall and break, potentially damaging the extraction pipes within the cavern.
“From an engineering and geomechanical standpoint, these concerns are highly valid,” Misra told Fortune in an email. “Salt is a highly dynamic rock type, and aggressively altering the fluids, pressure, and temperatures inside these deep caverns directly threatens their structural integrity.”
Despite the Department of Energy saying the minimum amount of oil to operate the SPR is 70 million barrels, Misra said the current reserve levels still present a real risk to the reserves, which will hit their legal limit of 252 million barrels in about three months if extraction moves at a conservative pace of 500,000 barrels per day. There’s also increased risk of physical damage, he said, including a layer of an oil-water-impurity sludge rising near the ceiling intake of the extraction system, which can destroy the surface pumps, as well as dissolution of the salt wall and thermal shock.
“We should be highly concerned about the integrity of the caverns anytime crude inventories drop below 300 million barrels,” Misra said. “At these depleted levels, the reserve physically loses its ability to pump oil at the rapid emergency speeds it was built to achieve without risking severe structural damage.”
