Most Australians could not find Kharg Island on a map. It is a strip of rock in the Persian Gulf, roughly 32 kilometres off the Iranian coast, and it handles close to 90 per cent of Iran’s crude oil exports. Almost nobody paying down a mortgage in Penrith or managing a self managed super fund in Toorak has ever given it a moment’s thought.
That may be about to change.
On the morning of 9 September, reports of explosions near Kharg Island, combined with Iran backed Houthi attacks on Saudi energy facilities, pushed Brent crude to a six week high of nearly US$100 per barrel. Within hours the Australian share market had surrendered its early gains and slid to a fresh six week low.
That sequence is not a coincidence. It is a transmission chain, and learning to trace it is one of the more useful things an investor can do, because it explains something that otherwise looks absurd.
The Australian economy is not booming. Consumer sentiment just fell off a cliff. Business conditions have turned negative for the first time in six years. Housing markets are softening. And yet the market now assigns roughly an 80 per cent probability to the Reserve Bank raising the cash rate on 29 September.
Weak economy. Higher rates. Those two facts appear to contradict each other.
They do not. The link between them runs through a small island in the Persian Gulf.
Why this matters now
Let us walk the chain, one link at a time, because each link is where an investor can get the analysis wrong.
The first link is supply risk, not supply loss. The Strait of Hormuz crisis has been running since late February 2026. Through it, before the conflict, passed roughly a fifth of the world’s seaborne oil. Traffic has not stopped entirely, but it has been repeatedly disrupted, and traders now price a permanent probability that it could stop. That probability, not the actual barrels lost, is what sets the price.
The second link is the inflation print. Energy costs sit inside almost every price in a modern economy. They move freight, they move food, they heat and cool buildings, and they feed into the cost of nearly everything a household buys. Australian headline inflation eased to 3.5 per cent over the twelve months to July, but the trimmed mean measure the Reserve Bank watches most closely held stubbornly at 3.6 per cent. Both remain above the 2 to 3 per cent target band.
The third link is the central bank. The Reserve Bank held the cash rate at 4.35 per cent in August. It has already been tightening through 2026. Governor Michele Bullock made clear the door remained open. Then June quarter GDP came in at 0.4 per cent for the quarter and 2.1 per cent for the year, stronger than several forecasters expected, and the market’s view changed within days. Pricing for a September hike moved from around 17 per cent before the July inflation data to roughly 80 per cent by Friday 6 September. All four major banks now forecast a hike before the end of the year. NAB has pencilled in 29 September and a move to 4.60 per cent.
The fourth link is the mortgage. A 25 basis point rise adds roughly A$76 per month to repayments on a A$600,000 variable rate loan.
The fifth link is the portfolio, and this is where most investors stop paying attention precisely when they should start.
What the market is pricing, and what it may be missing
This is not just an Australian story. Federal Reserve Chair Kevin Warsh delivered a notably hawkish address at Jackson Hole on 28 August, arguing that softer price data did not mean underlying trends had meaningfully improved. The market read it exactly as it was intended. The US 10 year Treasury yield has climbed to around 4.80 per cent, its highest since late 2023, and the September FOMC meeting became genuinely live for a rate increase for the first time in years.
So we have two central banks, on opposite sides of the Pacific, tightening into an energy shock they did not cause and cannot fix.
Here is where I think the consensus framing is too simple.
Markets are treating this as an inflation story. It is at least as much a growth story, and the growth damage is arriving before the inflation damage clears.
Look at the Australian evidence. The Westpac Melbourne Institute consumer sentiment index dropped 5.2 per cent in September to 84.4, back towards the deeply pessimistic levels seen earlier in the year. NAB’s measure of business conditions fell five points to minus 1, negative for the first time in six years, led by a ten point fall in profitability. Households are being squeezed by fuel costs and rate expectations at the same time. Businesses are being squeezed by input costs they cannot fully pass on.
An oil shock is a tax. It transfers income from oil consuming economies to oil producing ones. Australia is a net energy exporter in aggregate, which softens the national accounts, but the average household does not own an LNG train. The average household owns a car and a mortgage.
That is the part the headline inflation number does not capture. The economy is being tightened twice: once by the oil price, and once by the central bank responding to the oil price.
The second order effects are already visible in the market
You can see the repricing in the sector data, and it is worth reading it properly.
The information technology sector on the ASX 200 has fallen more than 12.5 per cent in three weeks. That is not a story about software demand. It is a story about discount rates. Long duration assets, where most of the value sits in cash flows a decade away, are the most sensitive to a rise in the risk free rate. When the 10 year yield moves, the present value of 2036 earnings moves more than the present value of 2027 earnings.
Financials fell 10.5 per cent across August. That is not the textbook reaction to higher rates, which usually flatters bank margins. It reflects something more considered: if the rate rise is being driven by an imported cost shock rather than domestic strength, the credit quality of the loan book matters more than the net interest margin.
Real estate investment trusts have been among the hardest hit sectors on down days. Higher discount rates and higher debt costs are a direct hit to asset values.
Energy and materials have held up better, for obvious reasons.
The pattern here is not random. The market is systematically repricing duration and leverage. That is exactly what you would expect it to do, and it is exactly what it did in 2022.
What history suggests, without pretending it repeats
There is a reasonable counter argument, and honest analysis has to make it.
Central banks have looked through supply shocks before, and they have often been right to do so. An oil price spike driven by geopolitical risk premium tends to decay quickly once the risk fails to materialise. Physical supply through Hormuz has been disrupted rather than eliminated. If the situation stabilises, the risk premium can drain out of the oil price faster than it went in, and the inflation impulse fades with it.
Gold offers a useful illustration of how violently these premia can move. It crossed US$5,000 an ounce for the first time in January 2026 and touched an intraday record above US$5,500, then retreated below US$4,000 by late June, and now trades around US$4,400. That is not the behaviour of a stable safe haven. It is the behaviour of an asset repricing a fear that keeps changing shape.
The labour market data is also more ambiguous than the headlines suggest. The US August jobs report showed 162,000 jobs added, roughly three times expectations. But the three month average sits closer to 71,000. One number screams strength. The other whispers slowdown. Both are true.
And a priced hike is not a delivered hike. Markets have been confidently wrong about central bank decisions many times before. Australia’s August labour force data lands on 24 September, five days before the Board meets, and the August inflation figures do not arrive until 30 September, the day after.
The Reserve Bank will make its decision with incomplete information. So will everyone trading around it.
What this means for a long term portfolio
None of this is a call to make heroic macro bets. Markets move in hours. Economies adjust in months. Portfolios should be built for the second timeframe, not the first.
For long term investors, the practical question is not whether the Reserve Bank moves on 29 September. It is whether your portfolio is positioned for a world where the risk free rate is structurally higher than the one most people spent 2024 and 2025 anticipating.
That question has a few components worth thinking about.
The first is duration. Assets whose value depends on distant cash flows have already repriced once. If yields stay elevated, they may reprice again. That does not make them bad businesses. It makes them businesses whose entry price matters more than it did.
The second is leverage. Companies that borrowed cheaply and now face refinancing at materially higher rates have a problem that has nothing to do with the quality of their product. Balance sheet strength has moved from a nice attribute to a load bearing one.
The third is pricing power. In an environment where input costs rise and consumers are under pressure, the businesses that survive comfortably are the ones that can pass costs through without losing volume. That is a question about competitive position, not about macroeconomics.
The fourth is your own timeframe. If you are a retiree drawing an income from a portfolio, a higher risk free rate is not purely bad news. Cash and fixed income are paying something again. That is a genuine change from the environment of five years ago.
The lesson is not to panic. It is to think clearly about what has actually changed, which is the price of money, and what has not, which is the value of owning good businesses at sensible prices over long periods.
TAMIM Takeaway
An oil shock that began in the Persian Gulf has travelled through freight costs, fuel bills and inflation prints, and arrived at the door of Australian mortgage holders and share portfolios. The market now prices a roughly 80 per cent chance of a Reserve Bank rate rise on 29 September, with all four major banks forecasting a hike before year end, and the US Federal Reserve facing a similar decision.
What the market may be underweighting is that this is a growth shock as much as an inflation shock. Consumer sentiment has collapsed to 84.4 and business conditions have turned negative for the first time in six years, while the tightening has barely begun to bite.
For long term investors, the useful response is not to forecast the next decision. It is to check whether the portfolio is built for a higher cost of capital: less tolerance for stretched duration, more attention to balance sheet strength, and a preference for businesses that can pass on costs rather than absorb them.
Rate decisions are events. Cost of capital is a regime. It is the regime that shapes returns over a decade, and it is the regime that has quietly changed while everyone waited for cuts that are not coming.