The engineering behind the US Strategic Petroleum Reserve

https://johnjwang.com/post/2026/09/15/engineering-behind-us-strategic-petroleum-reserve

So how did the US solve this? The crux was using salt domes at four sites in Texas and Louisiana along the Gulf of Mexico. The US created massive caverns underground in these salt domes that hold about 10 million barrels each (more than the entire Red Hill facility). The DOE currently lists 60 caverns with a combined authorized storage capacity of about 714 million barrels.

A few properties make this work:

• Cylindrical caverns are excavated using water. Engineers drill into a salt dome and inject fresh water. The salt dissolves in the water, and then pumps are used to remove the resulting brine, leaving a cavern that can be used to store petroleum.

• Salt contains the oil and helps seal small fractures. The rock salt surrounding the SPR’s caverns has extremely low permeability, meaning fluids have very little ability to pass through it. It also doesn’t react with petroleum. Under enormous pressures underground, salt also slowly deforms, which helps close small fractures. The salt itself can therefore contain the oil without a steel-and-concrete tank lining the cavern.

• Oil floats on water, which means pumping water into the bottom of the cavern pushes the oil out. As fresh water is pumped into the bottom of the cavern, the oil gets displaced upwards into a delivery system.

 

A bonus interesting comment from the discussion on Hacker News

There was a good comment on r/oil by someone who worked on the engineering for the SPR. Unfortunately it's fallen off the front page and I can't find it now, but:

> Also, the more water we pump in, the more salt leeches into the water and the more the bottom of the chamber deforms, creating shear forces in the upp walls that lower its overall structural integrity.

It turns out that it's trivially easy to prevent the water from leeching out the salt. They presaturate the water with salt, so that it already contains the maximum amount of salt that can be dissolved for a given temperature. When they pump the brine out, it goes into aboveground brine pools that can easily be seen on satellite imagery. The salinity of this brine can easily be controlled: if you want to expand the cavern, you mix it with freshwater so the brine dissolves more of the edges, if you don't you pump it back in as brine.

Edit: Here, found some satellite imagery of one of the SPR sites:

https://maps.app.goo.gl/B8XJ9TVhQfcdErky5

You can clearly see the brine pond, which is as big as the aboveground portion of the SPR itself.