The global story dragging Australian borrowers around by the collar is not a local housing headline at all. It’s a shipping lane: the Strait of Hormuz.

In early March, multiple independent trackers and news reports showed tanker movements collapsing to effectively nothing, with marine-traffic analysis describing a drop from the usual flow of large tankers “down to zero”. At the same time, producers in the region began to cut output because exports were constrained and storage was filling—one vivid example being reports of Iraq’s southern oilfield output falling sharply as storage hit maximum capacity.

By the morning of 9 March, oil-market volatility had turned into front-page, servo-forecourt reality: ABC News reported Brent crude surpassing US$115 per barrel during the day’s trade and petrol prices reaching well above $2/L in places, with wide variation by city and suburb.

The U.S. Energy Information Administration estimates that in 2024 around 20 million barrels per day of oil transited Hormuz or about 20% of global petroleum liquids consumption flows through Hormuz are more than one-quarter of global seaborne oil trade; it also notes that about 20% of global LNG trade transited the strait in 2024. The same EIA analysis highlights how Asia is disproportionately exposed (with most Hormuz crude and LNG headed to Asian markets), while US reliance on Persian Gulf crude imports is comparatively small.

Westpac’s core framing is that this is not “just” an oil price story. It’s a story about inflation psychology, household cash flow, and central bank reaction functions.

How a war headline reaches your mortgage statement

There’s three transmission lines from the Middle East to Australian financing costs.

1. Cash-flow squeeze. Petrol is one of the fastest prices to move from global markets into household budgets, and it’s highly visible, people literally watch the digits change on the bowser. Higher oil prices feed rapidly into headline inflation via petrol and transport costs, and can also flow indirectly via energy-intensive inputs like fertilisers. Commuters are seeing prices around (and above) $2/L in many places, and the story had tipped into anxiety behaviours like fuel hoarding and wholesale rationing.

2. Inflation expectations. The “belief layer” that sits between a one-off price jump and ongoing inflation. In a 3 March Q&A, Michele Bullock Governor of the Reserve Bank of Australia laid out the central bank problem in plain language: Australia is a net energy exporter in some respects, but also a net importer of oil; if petrol costs rise, households have less money for other spending, and if the shock is prolonged it can hit activity as well as inflation. She also underlined the complication that inflation was already elevated, which could make it harder to “look through” a supply shock if expectations start to drift.

3. Interest-rate and credit channel. The RBA’s own explainer on monetary policy transmission describes the basic pipeline: policy changes influence economy-wide interest rates, which then influence activity and inflation through channels including cash flow, asset prices, and the exchange rate. When markets think the RBA might need to lean harder against inflation risk, lenders and borrowers feel it through pricing, borrowing capacity, and credit appetite.

This is why, the Strait of Hormuz matters for loans even if you never buy a barrel of oil in your life.

Westpac’s big point: the oil shock is inflationary, but it’s also a growth shock

A subtle but crucial theme is that not all inflation is created equal.

Westpac’s economists are describing the first-round oil shock as a temporary supply shock: it lifts the price level, but that does not automatically mean ongoing inflation forever. Central banks often try to “look through” such shocks unless they see second-round effects (wages and broad pricing behaviour) or inflation expectations de-anchoring.

The Westpac team is putting numbers around “how big is big” for Australia and New Zealand under different disruptions:

• If only Iranian supply is affected, Westpac’s modelling suggested Australia’s CPI rises around 0.7 percentage points, with the near-term GDP impact marginal.
• If the Strait is disrupted for one month, the Australian CPI lift is around 1.0 percentage point, with GDP growth around 0.2 percentage points lower.
• A three-month disruption could see CPI temporarily spike around 1.5 percentage points at the peak, with GDP about 0.5 percentage points lower by end of 2026.

Australia has LNG and coal export exposure that can cushion national income and the currency, but that cushion does not fully neutralise the drag from higher fuel costs.

That matters for borrowers because it means we’re not looking at a neat, one-directional policy response (the simplistic “inflation up → rates up → mortgages up” chain). There is explicit weighing of two uncomfortable possibilities at once:

• The shock is brief enough that the right response is not to overreact with monetary tightening, because the price spike fades.
• Or the shock is prolonged—and then it becomes a messy mix of higher inflation and weaker growth, which is exactly the environment where “rate hikes fix everything” becomes a much less confident sentence.

The central bank is doing risk management under genuine uncertainty, not ticking boxes.

What this can do to financing and loans in the real world

Where the cash rate already sits, and what “live meetings” does to pricing. The RBA had already lifted the cash rate target to 3.85% in February, with Governor Bullock arguing inflation was too high and that the cash rate needed to respond. After that decision a follow‑up hike in March was not the base case, with May viewed as more likely if inflation validated the RBA’s concerns. But the Middle East shock added a new wrinkle, and Bullock publicly warned that markets should not assume the RBA only moves on “quarterly CPI” meetings; “every meeting is live”, including the 16–17 March meeting.

1. When a meeting is “live”, pricing can shift before any decision is made. That is one reason borrowers often feel rate uncertainty as stress even before lenders change advertised rates: fixed-rate pricing, credit spreads, and lender appetite can all react to updated risk views.

2. The difference between variable and fixed borrowing in the RBA’s Bulletin has documented how policy-rate changes pass through to outstanding mortgage rates through the cash‑flow channel, albeit with lags that can vary depending on competition and the share of borrowers on fixed rates. In a volatile environment, that means a borrower’s experience can differ sharply depending on product type and repricing timing especially if households are simultaneously hit by higher petrol bills.

3. Borrowing capacity and approvals is not just repayments. Even if your current rate doesn’t move immediately, new credit is assessed under prudential rules that build in buffers. The Australian Prudential Regulation Authority confirmed that the mortgage serviceability buffer remained at 3 percentage points, which mechanically reduces maximum borrowing power when interest rates are high or expected to rise. APRA also introduced a debt‑to‑income “guardrail” (from 1 February 2026) limiting the share of new mortgages written above six times income, intended to restrain riskier lending as housing-related vulnerabilities build.

In plain terms: even if Westpac is right that the RBA should be cautious about overreacting to a supply shock, the household credit machine is already set to “tight”, and sudden energy-price volatility tends to make lenders more conservative at the margin.

4. The business lending angle is easy to miss if you only watch mortgages. When oil supply is constrained, the story seldom stays confined to fuel retail. Reuters reporting described producers cutting output as storage filled and exports were disrupted, while tanker traffic and shipping alternatives were constrained and more expensive. That mix typically shows up in business borrowers as higher and more variable input costs (fuel, freight, and sometimes energy), and increased working-capital needs; exactly the kind of environment where banks start asking tougher questions about cash‑flow resilience.

The domestic backdrop matters just as much as the war

“The war hits an economy that already has its own complicated story”.

On the domestic data, the Australian Bureau of Statistics reported that Australia’s GDP grew 0.8% in the December quarter 2025 and 2.6% through the year, with growth across almost all industries and both public and private demand contributing. Westpac’s chief economist similarly characterised the economy as being in a cyclical upswing, broadening beyond one or two narrow drivers.

But Westpac also flags a tension that is directly relevant to loans: even in an upswing, the consumer can be “reined in” when inflation is high and policy is restrictive. Q4 consumption was weaker than expected, and the likely private sector recovery is more investment led than consumption led; households are dealing with higher petrol prices and a rising tax burden.

This matters for financing in two ways.

1. Weaker consumption makes lenders more alert to downside scenarios for household cash flow even if employment is still decent, because repayment stress often shows up first as households cut discretionary spending.

2. Supply capacity may be better than feared, partly due to data revisions and better productivity outcomes. In particular, the productivity growth running around 1.0% year‑ended, above the RBA’s February assumptions. If productivity and labour supply are better than the pessimistic baseline, the economy can grow faster without generating as much inflation pressure which, should reduce the need for the RBA to “hammer inflation regardless” in response to every new shock.

In a separate February note on full employment, the Westpac chief economist argues that “full employment” is harder to pin down than inflation, and that the RBA’s estimate of the sustainable unemployment rate (its NAIRU‑style concept) is inherently uncertain. She contrasts a view where potential growth is just above 2% and sustainable unemployment is around 4.6% with an alternative (closer to Westpac’s view) where potential growth is more like 2.25–2.5% and sustainable unemployment more like 4.25%.

For borrowers, this is not academic trivia. If the RBA believes the economy has less supply capacity and unemployment is “too low”, it will be more inclined to keep policy restrictive (or tighten it) to protect the inflation target. If Westpac is right that capacity is higher, the RBA can afford more patience especially when a shock is likely to be growth-negative as well as inflationary.

So what’s the bottom line for loans?

The through-line is that this is a two-sided shock, and that distinction is the key to making sense of what happens to financing costs.

If the Strait disruption proves brief, logic suggests the RBA could rationally try to look through a temporary price-level jump because the main damage is to real household income, not a permanently higher inflation trend. In that world, the most immediate borrower impact is the painfully simple one: higher petrol and transport costs crowd out other spending, and households feel “tighter” even if their interest rate doesn’t change immediately.

If the disruption persists, there will be materially higher CPI outcomes and weaker growth. That is the environment where lending can tighten in more than one way at once: not only through interest-rate expectations, but through stricter credit assessment as lenders and regulators focus on resilience.

Either way, the shared message from Westpac and the RBA is that inflation expectations are the tripwire. Westpac notes petrol’s salience and urges keeping the risk in perspective rather than reacting to a mere possibility, while the RBA is explicit that if expectations move, policy will respond.