UKOilWatch Analysis — the financial mechanism most likely to transmit the energy shock into global markets, and the single signal that would show it had begun.
Most people would not immediately connect a disruption in the Strait of Hormuz with the price of American technology shares, European government bonds or emerging-market currencies.
The connection runs through Japan.
For decades, Japan has provided the financial world with something extraordinarily valuable: cheap money. Investors have been able to borrow Japanese yen at low interest rates, exchange those yen for dollars or another currency, and invest the proceeds in assets offering higher returns.
This is known as the yen carry trade.
It sounds technical, but the principle is straightforward. Imagine borrowing money at 1%, placing it somewhere that pays 4%, and keeping the difference. Provided the exchange rate remains stable, it can be a relatively predictable way of making money.
The danger begins when thousands of investors make the same bet with borrowed money — and then all try to leave at once.
Japan's energy vulnerability could help produce exactly that situation. Not, as is often assumed, by driving the yen down through the import bill — but by making Japanese inflation politically intolerable, and so forcing the authorities to act.
The world's cheap-money machine
The Bank of Japan's short-term policy rate is around 1%: in June 2026 the BoJ instructed that the uncollateralised overnight call rate remain at about that level. The Federal Reserve's target range is 3.5% to 3.75%, leaving a headline US–Japan policy-rate gap of roughly 2.5 to 2.75 percentage points.
That gap encourages banks, hedge funds and other investors to borrow yen cheaply, sell those yen for dollars, buy higher-yielding bonds, shares or currencies, and collect the difference.
An important qualification: that is the headline gap, not the guaranteed profit on a carry trade. Actual returns depend on funding costs, hedging, leverage and — decisively — currency movements.
The trade works particularly well when the yen is falling, because the investor repays the loan in a currency that has become cheaper.
But it contains a hidden weakness. A few percentage points of annual income can be wiped out by a much faster movement in the exchange rate. If the yen appreciates 5% in a week, an investor earning perhaps 3% over an entire year can suddenly face a substantial loss.
Leverage makes this more dangerous. Investors may have borrowed many times their own capital, so a manageable currency movement becomes a margin call — forcing them to sell assets immediately.
Why energy matters to the yen — and what it actually does
Japan is not merely another large energy consumer. It is one of the developed world's most import-dependent energy systems.
Japan's energy self-sufficiency rate is approximately 15.3%, the lowest in the G7. Roughly 69–70% of its electricity generation still depends on fossil fuels. And it relies on the Middle East for more than 90% of its crude-oil imports — around 2.36 million barrels a day.
Its exposure is not only oil. Japan is one of the world's largest LNG buyers, and Hormuz disruption has removed more than 300 million cubic metres a day of Qatari and Emirati LNG from the market since March. That forces Japan to compete directly with European utilities for the same flexible Atlantic cargoes — the very scramble we describe in Europe Is About to Sanction Itself. Japan and Europe are, increasingly, bidding against each other for the molecules neither can do without.
Here it is worth being precise about the causal chain, because it is easy to overstate.
The intuitive story runs: higher energy prices mean a larger import bill, more demand for dollars, and therefore a weaker yen. That channel is real, but it is second-order. Day to day, the yen is driven far more by interest-rate differentials and expectations about Bank of Japan policy than by the trade balance.
Energy's real work is different, and more dangerous. It is an amplifier and a political catalyst.
The evidence is in the price data. Japan's import-price index rose 29.7% year on year in June measured in yen, compared with 17.8% in contract-currency terms — and 1.3% month on month in yen against just 0.1% in contract currency. In other words, roughly two-thirds of the year-on-year shock is the world price; the rest is the currency. A weak yen is not merely a symptom of the energy shock. It is substantially magnifying it inside Japan.
That is what turns an external price problem into a domestic political one. Imported inflation reaches households and businesses, pressure builds on the government and the Bank of Japan to defend the currency — and it is that response, not the import bill, which threatens the carry trade.
One honest complication, often ignored: the feedback runs both ways. A stronger yen would reduce the cost of Japan's imported energy, easing the very inflation that prompted intervention. Japan is not trapped in a pure doom loop — there is a stabilising force in the system. The risk is not that the yen must fall forever; it is that the transition from weak to strong, when it comes, may be violent enough to force leveraged investors out all at once.
The first stage can strengthen the carry trade
Here lies the apparent contradiction.
An energy crisis does not necessarily cause the carry trade to unwind immediately. At first, it may make the trade more profitable.
Higher energy prices weaken Japan's trade position. A weaker trade position adds to the pressure on the yen. A falling yen benefits the investors who borrowed yen and deployed the money elsewhere.
The early sequence therefore looks like this:
Energy disruption → oil and LNG rise → yen weakens → carry traders make money → more investors join the trade.
This is why a visibly deteriorating Japanese energy position can coexist with a thriving yen carry trade.
But it also builds a larger imbalance. The further the yen falls, the more expensive Japan's imported energy becomes; the more expensive energy becomes, the greater the inflationary pressure on households and businesses; and the greater that pressure, the stronger the political case for defending the currency.
The trade grows strongest at precisely the moment the conditions for its reversal are being created.
The second stage is where the danger begins
The carry trade fails when investors no longer believe the yen will remain cheap and weak. Several events could change that calculation: direct currency intervention; an unexpected Bank of Japan rate increase; falling American interest rates; a global equity decline; a banking or credit shock; or a rapid rise in volatility.
Japan has already intervened heavily to support its currency. Reuters, citing people familiar with the authorities' thinking, has reported that Japan was moving toward less predictable intervention tactics designed to catch short-yen traders off guard — avoiding advance signals and fixed exchange-rate thresholds. This is reported practice, not an officially declared programme, and the distinction matters: the uncertainty is itself the tool.
Intervention alone may not permanently reverse the yen. But it can produce the initial movement that forces leveraged traders to cut positions.
Once that begins, the trade runs backwards. Investors sell the shares, bonds or other assets bought with borrowed yen; they convert the proceeds back into yen; they use those yen to repay their loans. That buying pushes the yen higher still.
Yen rises → carry trades lose money → investors buy yen to repay loans → yen rises again → more investors are forced out.
This is the point at which a currency movement becomes a global liquidation event.
We have already seen a warning
The mechanism is not theoretical.
In August 2024, the Bank for International Settlements concluded that market turbulence was amplified by leveraged deleveraging, higher margin demands and a partial unwinding of yen-funded carry trades. Leveraged equity, currency and options strategies were forced to unwind; yen-funded currency carry trades were among the hardest hit; the TOPIX fell 12% on 5 August alone. The BIS later described the episode as a partial but sudden unwinding that transmitted tighter financial conditions from Japan into the United States through leveraged speculative investors.
Crucially, the BIS did not present the carry trade as the sole original cause — it was the amplifier.
On size, the BIS offered a rough central estimate of around ¥40 trillion, or roughly $250 billion, in relevant carry exposure entering that episode — while cautioning that data gaps probably made the figure too low.
That caveat is the point. No one knows the true total, because the exposure is spread across banks, currency markets, derivatives, hedge funds, corporate borrowing and investments never publicly labelled as yen-funded. Markets may not learn how much leverage exists until falling prices reveal who borrowed too much. And the 2024 episode — violent as it was — was explicitly only a partial unwind.
How energy could become the cause
An energy crisis could move from being a Japanese trade problem to being the cause of a carry-trade reversal through several stages.
First, prolonged interruption to Middle Eastern oil and LNG supplies raises Japan's import bill and adds to pressure on the yen. Second, the weaker yen magnifies the cost of fuel, electricity, transport, food and industrial materials inside Japan — as the 29.7%-versus-17.8% gap already shows. Third, inflation rises while activity weakens, and Japan faces a form of stagflation. Fourth, the Bank of Japan comes under pressure to raise rates, or the government intervenes directly. Fifth, the interest-rate advantage behind the carry trade narrows — or traders begin to fear it soon will. Sixth, a strengthening yen forces leveraged investors to close positions. Finally, the assets bought with those borrowed yen are sold into already nervous markets.
Energy would not simply be one more piece of bad news. It would be the initiating force in a financial cascade.
Why oil markets should care
At first glance, the collapse of a currency trade might appear separate from the physical oil market. It is not. Carry-trade investors do not hold only currencies; borrowed money flows into government bonds, equities, emerging markets, commodity companies, credit and derivatives. When those positions close, investors sell what they can — not necessarily what caused the problem.
Oil could fall despite a physical shortage. A financial liquidation can push crude lower even while physical supply stays tight. Funds facing margin calls may sell profitable oil positions to cover losses elsewhere. The resulting decline could be misread as evidence the energy crisis had eased, when it reflected forced selling.
Energy shares could be hit. Producers may benefit from higher crude, but their shares can still fall in a broad liquidation — investors needing cash sell liquid assets, including profitable ones.
Credit could tighten. Refiners, shipping companies, commodity traders and smaller producers depend heavily on credit. A carry-trade shock could push lenders to reduce risk, raise collateral requirements and charge more — leaving the physical energy system facing a credit shortage at the same time as a supply shortage.
Hedging costs could rise. Airlines, utilities, manufacturers and fuel distributors hedge against price moves. In extreme volatility those hedges demand more collateral, so a company can be economically protected against higher prices and still face an immediate cash crisis.
Asian demand could weaken. A serious financial shock would damage Japanese and regional activity, reducing industrial output, transport and consumption — and therefore oil demand after the initial price surge. The market could move rapidly from fearing insufficient supply to fearing collapsing demand.
The central-bank trap
The Bank of Japan would face an almost impossible choice.
Leaving rates unchanged could allow the yen to weaken further, increasing imported inflation. Raising rates could support the currency, but would raise borrowing costs across an economy carrying enormous public debt and weaken businesses already struggling with energy costs. Direct intervention could provide temporary relief, but might trigger the very carry-trade squeeze policymakers wish to avoid.
Doing nothing carries risk. Acting carries risk. And delaying may allow the position to grow larger.
The warning signs to watch
The most important indicator is not simply whether oil rises or the yen falls. During the first phase of the crisis, those two movements are likely to occur together.
The dangerous signal is different:
oil remains expensive, global markets begin falling, and the yen suddenly strengthens.
That would suggest investors were no longer treating Japan's energy weakness as a reason to sell the yen. Instead they would be buying yen to close borrowed positions.
UKOilWatch readers should therefore monitor:
- the oil price measured in yen, not only in dollars;
- sharp yen appreciation during falling equity markets;
- Japanese currency intervention;
- unexpected Bank of Japan policy changes;
- falling US Treasury yields;
- weakness in technology shares and other crowded positions;
- sudden increases in market volatility;
- tighter credit conditions for commodity and shipping companies.
No single indicator proves the carry trade is collapsing. The danger comes when several appear together.
The hidden connection
The yen carry trade is often presented as an obscure strategy understood only by professional traders. In reality it is a mechanism through which cheap Japanese money supports asset prices around the world.
Japan's dependence on imported energy creates a potential fault line beneath that mechanism. An energy shock weakens the yen and initially rewards those betting against it — but the same shock raises inflation, damages Japan's economy and increases the pressure for government or central-bank action.
The system can therefore move from stability to instability with extraordinary speed.
The greatest warning will come when the yen stops behaving as an energy-importer's currency. As long as oil rises and the yen weakens, the carry trade remains under strain but continues to function. When oil remains high, markets fall and the yen begins rising anyway, the repayment phase may have begun.
At that point, the issue will no longer be confined to Japan.
The world may discover that an energy crisis has reached through the currency markets, pulled away a major source of global liquidity — and forced everyone who borrowed cheaply to find the exit at the same time.
This is the worked example beneath The World Is a Pressure Cooker, which sets out the wider frame: energy as the flame, sovereign debt as the vessel, and collateral as the likeliest point of fracture. For the economics of why concentrated, "efficient" systems break this way, see Why Cheap Energy Isn't Always Cheap.