Strategic Reserves: Buying Time, Not Solving Shortage
Holding a large quantity of fuel that you hope never to use is an odd thing for a state to do, and it survives because the alternative was demonstrated in 1973. What has been contested ever since is not whether reserves should exist, but what they are for.
Where the 90-Day Rule Came From
The International Energy Agency was created in 1974 by oil-importing countries responding to the embargo. Its founding obligation is that each member holds emergency reserves equivalent to 90 days of the previous year's net imports, and participates in a coordinated release when the agency declares a collective action.
The coordination matters more than the volume. A single country releasing stock into a tight market would mainly subsidise its own consumers while the world price barely moved. Several countries releasing at once changes the global balance, and the announcement alone can cool a market that is pricing in panic.
Net imports is the right denominator, which produces an outcome that surprises people. An exporting country has no obligation, because its exposure is to the price rather than to availability, and countries that reduce their import dependence see their obligation fall automatically.
Collective releases have been declared only a handful of times - the 1991 Gulf war, Hurricane Katrina in 2005, the Libyan disruption in 2011, and the largest of all in 2022. The rarity is deliberate. A reserve used routinely is not a reserve, and part of its effect comes from the market believing it is held for genuine emergencies.
How the Oil Is Actually Stored
The United States Strategic Petroleum Reserve holds oil in underground salt caverns along the Gulf Coast. The caverns are made by drilling into a salt dome and pumping in fresh water, which dissolves the salt and is removed as brine, leaving a void that can hold tens of millions of barrels.
Salt is close to ideal for this. It is impermeable, so oil cannot escape; it is self-sealing, because the rock slowly deforms and closes fractures; and the caverns cost a small fraction of what steel tanks of the same capacity would. The disadvantages are geographic - salt domes are where they are - and operational, since withdrawal is limited by how fast water can be pumped in to displace the oil.
That withdrawal rate is a real constraint. A reserve that holds a large volume but can only release a modest daily flow covers a slow disruption well and a sudden one poorly. Release capacity, not just stock, is what determines usefulness, and it declines as caverns empty.
Other countries hold stock differently: in conventional tank farms, in leased commercial storage, or as an obligation placed on refiners and importers to maintain minimum inventories. Japan combines state-owned stock with industry obligations. The industry-obligation model is cheaper for the state and gives it less direct control in a crisis, which is the trade-off each country resolves differently.
What a Reserve Cannot Do
The recurring political temptation is to use reserves against high prices rather than against shortage, and this does not work for a structural reason rather than an ideological one.
A release adds supply temporarily. Traders know the volume is finite and that the reserve must eventually be refilled, which means future demand. The forward curve adjusts, and the spot effect is usually modest and short-lived. The 2022 release was the largest in history, and its price effect was real, contested, and far smaller than the volume alone would suggest.
Refilling is the part that gets less attention and matters most. A reserve released at a high price and refilled later is a public loss if the price has not fallen by then, and governments have repeatedly found refilling politically harder than releasing, since there is no visible crisis to justify the expenditure. Reserves in several countries sat well below their statutory levels for years afterward.
The honest statement of what a reserve does is narrow and worth keeping: it converts an acute physical shortage into a manageable one for a period of weeks to months, during which markets can reroute cargoes, alternative suppliers can raise output and diplomacy can operate. That is a genuine and valuable function. It is not price control, and it is not a substitute for diversity of supply.
Gas, and Now Minerals
Gas is harder to stockpile than oil. It occupies far more volume per unit of energy, and storage means depleted fields, aquifers or salt caverns rather than tanks. Most European gas storage was commercially operated, which meant it was filled according to the seasonal price spread rather than to any security standard - and in 2021, when that spread was unattractive, several facilities entered winter unusually empty.
The European Union responded in 2022 by mandating filling targets, a direct application of the oil reserve logic to a commodity where the market had been left to decide. Whether mandated filling raises the average purchase price is a genuine open question: buying to a schedule rather than to a price signal means buying when others are also buying.
The newest extension is to critical minerals. Several countries have announced stockpiles of rare earths, lithium or cobalt on the reasoning that supply is geographically concentrated, as oil was in 1973.
The analogy is imperfect in a way worth stating. Oil is consumed once and must be continuously resupplied, so a buffer directly offsets a flow interruption. A mineral is embedded in equipment that lasts twenty years, so a shortage delays new construction rather than stopping existing operation, and recycling eventually returns the material. The right size and purpose of a mineral stockpile are therefore different from an oil reserve, and the countries building them are still working out what that means.
Frequently asked questions
What is a strategic petroleum reserve?
A state-owned stock of crude oil held against supply interruption. International Energy Agency members are obliged to hold emergency reserves equal to 90 days of the previous year's net imports and to release them in coordination when a collective action is declared.
Why is oil stored in salt caverns?
Because salt is impermeable so oil cannot escape, self-sealing since the rock slowly closes fractures, and far cheaper than steel tanks of equivalent capacity. The caverns are created by pumping fresh water into a salt dome and removing the resulting brine. Withdrawal speed is limited by how fast water can be pumped back in.
Can releasing reserves lower fuel prices?
Only modestly and briefly. Traders know the released volume is finite and that the reserve must eventually be refilled, which represents future demand, so the forward curve adjusts. The 2022 release was the largest in history and its price effect was far smaller than the volume alone would suggest.
Why does refilling a reserve matter?
Because a reserve released at a high price and refilled before the price falls is a public loss, and governments repeatedly find refilling harder than releasing since no visible crisis justifies the spending. Several countries' reserves sat well below statutory levels for years after the 2022 release.
Do mineral stockpiles work like oil reserves?
Not exactly. Oil is consumed once and needs continuous resupply, so a buffer offsets a flow interruption directly. A mineral is embedded in equipment lasting decades, so a shortage delays new construction rather than halting existing operation, and recycling eventually returns the material - which changes both the right size and the purpose of the stockpile.
