GRID · FIELD GUIDE
The Strategic Petroleum Reserve — The World's Largest Emergency Oil Stockpile
Somewhere under the Texas and Louisiana coast, in caverns big enough to swallow skyscrapers, sits the largest emergency oil supply on Earth. It was built so a single embargo could never again hold a country to ransom — and right now it's emptier than it has been in forty years. So what is the Strategic Petroleum Reserve, why is the oil kept in salt, and what does it mean that it's draining fast?
Most maps of energy show the things that make power — turbines, panels, power plants. This one shows something stranger and more deliberate: a national insurance policy, kept as crude oil, buried in salt.
The Strategic Petroleum Reserve is the largest emergency oil stockpile on Earth. It exists because of a single shock. In 1973, an oil embargo cut supply to the United States almost overnight, prices quadrupled, and a country that had taken cheap energy for granted discovered it had almost no cushion. The response, written into law in 1975, was to build one: a vast government reserve of crude oil that could be released in a crisis. Half a century later it holds about 714 million barrels of capacity — and, right now, it's emptier than it has been in forty years.
The oil is kept in salt
The reserve isn't a row of tanks. It's about 60 caverns hollowed out of natural salt domes beneath the Gulf Coast, thousands of feet underground.
Making one is almost elegant. Drill a well into the salt, pump in fresh water, and the salt dissolves; pipe the brine away and you're left with a clean, precisely shaped cavity. It takes roughly seven barrels of water to make room for one barrel of oil. Salt is close to the perfect material for the job — crude can't seep through it, and at depth the rock behaves so slowly that any crack simply closes itself under pressure. The store seals itself, and it costs a fraction of what building tanks above ground would. A single cavern can be a cylinder some 200 feet across and 2,500 feet tall — tall enough to stand a skyscraper inside — holding around 10 million barrels.
Four sites, sized on the map
The reserve is split across four sites, and on the map each is drawn as a salt-cavern mark sized by its authorized capacity:
- Bryan Mound — the largest, near Freeport, Texas
- West Hackberry — near Lake Charles, Louisiana
- Big Hill — near Beaumont, Texas
- Bayou Choctaw — the smallest, near Baton Rouge, Louisiana
They cluster on the Gulf Coast for a reason: that's where the densest concentration of US refineries and crude pipelines sits, so oil released from the caverns can reach the places that turn it into fuel quickly.
One honest note about the sizing. The Energy Information Administration publishes the reserve's total inventory for the whole country, weekly — but not a live barrel count for each site. So this map sizes the marks by capacity, a fixed and published figure, and shows the live fill only at the national level. We'd rather show a true national number than a made-up per-cavern one.
Why it's draining now
The reserve filled steadily for decades and peaked at about 727 million barrels around 2009. Then came two drawdowns. In 2022, to blunt the price spike after Russia's invasion of Ukraine, the US sold a record volume of SPR crude. It was partly refilled — and now it's falling again, under a 2026 emergency exchange tied to the conflict with Iran, dropping on the order of 8–10 million barrels a week to around 331 million barrels, near 46% of capacity.
It's tempting to read that as the system failing. It isn't — releasing oil in a crisis is precisely what an emergency reserve is for. What's worth watching is simply the level: the cushion that 1973 taught the country to keep is now thinner than it has been in four decades.
Site data from the U.S. Department of Energy; the live national fill from the U.S. Energy Information Administration's Weekly Petroleum Status Report. Both are public-domain U.S. Government sources. The marks are sized by authorized capacity, not current fill, and the live fill is a national total only.
Frequently asked questions
What is the Strategic Petroleum Reserve, and what does this map show?
The Strategic Petroleum Reserve, or SPR, is the United States' emergency stockpile of crude oil — the largest government-held oil reserve in the world. It holds roughly 714 million barrels of authorized capacity in about 60 underground salt caverns, grouped across four sites along the Gulf Coast of Texas and Louisiana. The country built it after the 1973–74 Arab oil embargo, when an overnight cut-off sent prices spiralling and exposed how little buffer it had. The idea is simple: keep a vast reserve underground so that if a war, disaster or embargo chokes off supply, the government can release crude to refineries and steady the market. This map shows the four storage sites themselves, drawn as salt-cavern marks sized by their capacity, with the live national fill level pulled from the US Energy Information Administration.
Why is the oil stored in salt caverns?
Because salt is almost perfectly suited to holding crude oil cheaply and safely. The Gulf Coast sits over natural salt domes — huge plugs of rock salt pushed up from deep underground. To make a storage cavern, engineers drill a well into the salt and pump in fresh water; the water dissolves the salt and the resulting brine is piped out, leaving behind a clean cavity of precise dimensions. It takes about seven barrels of water to carve room for one barrel of oil. Salt has two properties that make it ideal: it's impermeable, so crude can't seep through it, and at those depths it behaves almost like a slow liquid — any crack closes itself under the surrounding pressure, so the store is naturally self-sealing. A single cavern can be a cylinder roughly 200 feet wide and 2,500 feet tall, holding around 10 million barrels — and creating that space underground costs a small fraction of what an equivalent tank farm would.
Why is the reserve at a 40-year low?
The reserve filled steadily for decades and peaked at about 727 million barrels around 2009. The big change came in 2022: to fight the price spike that followed Russia's invasion of Ukraine, the US sold a historic volume of SPR crude into the market, pulling the level down sharply. It was partly refilled afterwards, but it is falling again now — under a 2026 emergency exchange tied to the conflict with Iran, the reserve has been drawing down on the order of 8 to 10 million barrels a week, to around 331 million barrels. That's near 46% of capacity, the lowest level since the 1980s. It's worth being clear-eyed here: drawing the reserve down in a supply crisis is exactly what it's for — that's the point of an emergency stockpile. What's notable is simply how low the buffer now sits, and how quickly.
Why does this map size the sites by capacity instead of how full they are?
Because how full each individual site is isn't public information. The Energy Information Administration reports the SPR's total inventory for the whole country — one national number, updated weekly — but it does not publish a live barrel count for each of the four sites. So rather than invent a per-site fill we don't have, this map does the honest thing: it sizes each salt-cavern mark by the site's authorized capacity, which is a fixed, published design figure, and shows the live fill only at the national level, in the legend and on this page. You get a true sense of which sites are biggest, and a true national fill — without a fabricated per-cavern inventory dressed up as fact.
Where does the reserve fit in the journey of oil?
Think of it as a shock absorber sitting in the middle of the oil chain, not a producer. Upstream are the oilfields and imports that supply crude. Downstream are the refineries that turn crude into petrol, diesel and jet fuel. The SPR sits between them: in normal times it just holds oil; in a disruption, the government can release crude from the caverns to refineries to keep fuel flowing and prices from spiking. That's why the four sites cluster on the Gulf Coast — right next to the densest concentration of US refineries and the pipelines that connect them. On this Grid you can follow that chain directly: the oil and gas fields where crude is produced, the refineries where it's processed, and the pipelines that move it.
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