Issue 065 - Energy security - Emergency stock drawdown
How much time can emergency oil reserves buy?
The IEA says about 20 million barrels per day of crude oil and oil products passed through the Strait of Hormuz in 2025. Suppose a disruption cuts that flow in half.
Energy and infrastructureAbout 1 minute
Sources checked October 1, 2026. Figures and circumstances may have changed.
The problem
If a Strait of Hormuz disruption removed about 10 million barrels per day from the market, roughly how long could government-controlled emergency oil reserves cover that missing supply?
Also keep a second question in mind: even if the oil exists in storage, can it be released quickly enough to replace the missing daily flow?
Because Fermi problems target an order of magnitude, I normally use no more than two significant digits and write most calculations in scientific notation; the Fermi reference explains both conventions.
Grounding facts
The IEA's Strait of Hormuz factsheet puts 2025 flows at about 20 million barrels per day, including crude oil and products. Cutting that in half creates a missing-flow estimate of:
missing supply
~= 20 million barrels/day x 1/2
~= 10 million barrels/dayFor inventory, the cleanest public anchors point to a few different definitions:
IEA emergency stockpiles: IEA members held more than 1.2 billion barrels of emergency stockpiles, plus another 600 million barrels of industry stocks held under government obligation, when they announced the March 2026 coordinated release.
EIA strategic-inventory estimate: EIA's August 2026 Global Energy Security Data listed selected strategic inventories including about 1.49 billion barrels in China, 321 million in the United States, 187 million in Japan, and smaller volumes elsewhere. Those listed countries sum to roughly 2.5 billion barrels, and EIA notes the largest listed countries account for about 70% of global totals under its methodology.
Release rate: the same IEA emergency response did not instantly replace a 10-million-barrel-per-day shortfall. IEA said the collective action was bringing about 2.5 million barrels per day to market in May.
After checking sources
Checked answer and calculation
Start with the simplest inventory-only calculation. If you count IEA emergency stockpiles plus obligated industry stocks:
IEA emergency and obligated stocks
~= 1.8 x 10^9 barrels
coverage at 10 million barrels/day
~= 1.8 x 10^9 / 1.0 x 10^7
~= 1.8 x 10^2 days
~= 6 monthsIf you use EIA's broader strategic-inventory lens and scale its selected-country table to a rough global total, the inventory looks closer to:
strategic inventories worldwide
~= 3 x 10^9 barrels
coverage at 10 million barrels/day
~= 3 x 10^9 / 1.0 x 10^7
~= 3 x 10^2 days
~= about 1 yearBut that is the size of the tank, not the flow through the emergency spigot. The actual 2026 IEA action made 400 million barrels available:
announced emergency release
~= 4 x 10^8 barrels
full-deficit equivalent
~= 4 x 10^8 / 1.0 x 10^7
~= 40 daysAnd the reported release rate in May was about:
release-rate coverage
~= 2.5 million barrels/day / 10 million barrels/day
~= 25% of the missing flowSo the best scale answer is: emergency reserves can buy months, perhaps approaching a year under a very broad inventory definition, but they are not a multi-year fix. More importantly, actual release capacity may cover only a fraction of a 10-million-barrel-per-day shock. Inventory and delivery rate are different bottlenecks.
Before checking sources
Matt's original estimate
This is the unverified estimate Matt wrote before checking sources, not the checked answer.
I don't have strong intuitions about worldwide oil reserves, so I took a guess that the US oil reserves are in the range of about 200 million barrels, or 2 x 10^8, and that US oil reserves account for about 4% of all worldwide oil reserves, which means that might be about 5 x 10^9 barrels.
If the current flow of oil through the Strait of Hormuz is about 20 million barrels of oil daily, and half of that is restricted, that's 10 million barrels daily and 70 million weekly, about 7 x 10^7 barrels.
My intuition is that the worldwide governments might be able to mobilize 1% of their current reserves for economic easing due to the restricted oil flow, which is about 5 x 10^7 barrels - less than the weekly deficit, but close. At that rate, and assuming no changes, worldwide reserves would be wiped out in about 100 weeks, just under 2 years, while not fully resolving the deficit during that time.
Reasoning score
Matt's reasoning score: 85 / 100
Higher is better: earn points for useful facts, a sound reasoning approach, correct math, and a final estimate close to the sourced answer. The owl meter shows percent full of it: 100 minus the reasoning score.
Useful facts: 20/30. The U.S. reserve estimate was low but close enough, the global reserve estimate was high but still within order-of-magnitude range, and the missing-flow calculation started from the right 10-million-barrel-per-day gap.
Reasoning approach: 30/30. The core model was right: compare the size of the inventory with the daily shortfall, then separately consider how much can actually be mobilized.
Math: 5/10. The arithmetic was mostly fine, but the weekly release and total depletion discussion blurred full replacement versus partial replacement.
Final estimate: 30/30. The conclusion was well calibrated: reserves can help for months, but release rates probably do not fully cover a major Hormuz shortfall and the cushion is not a years-long solution.
Post-check reflection
Matt's reflection
Looks like my intuition about US reserves was low, but worldwide reserves was high - still within an order of magnitude of both. Looks like US reserves are a significant percentage of worldwide reserves.
Also looks like my intuition about mobilization rate of the inventory was high, but again within an order of magnitude.
My final answer seems consistent with real world data: that the mobilization rate probably wouldn't cover the regular shortfall, and that inventory won't last more than a year if it was fully covering the shortfall and not much longer than two years if being mobilized at the maximum rate.
This all supports the importance of the news item generally.
Recommended memory peg
Remember emergency oil stocks as a months-scale buffer: roughly 1 to 3 billion barrels under common strategic-reserve definitions, while a 10-million-barrel-per-day disruption burns through 300 million barrels per month.
Reader results
Bars show how submitted estimates sort into the answer choices from the gut-check prompt.