Westpac Warns Oil Shock's Inflation Spillover Could Force RBA to 17-Year Rate Peak

The core driver of Westpac's revised outlook is a historic supply shock. The conflict in the Middle East has effectively closed the Strait of Hormuz, the world's most critical oil chokepoint, for an estimated eight weeks. This single disruption has triggered the largest supply disruption in the history of the global oil market, halting around 20 million barrels per day of crude and products that normally flow through the strait. The scale of the shock is now the new baseline.

The inflationary pressure is immediate and severe. The benchmark Brent crude price has jumped 51% since the start of March, trading above $116 a barrel. This surge has been brutal for consumers, with fuel costs spiking sharply. The market's reaction was swift, with prices climbing even after a coordinated release of 400 million barrels from emergency reserves. The expectation gap here is stark: the market had not priced in a disruption of this magnitude or duration.

Westpac's analysis shows the shock is not just a headline number; it's feeding through into the broader economy faster than expected. The bank notes a rapid pass-through of higher fuel and oil-derived costs into broader Australian prices. This "second-round" effect is critical. It means the inflationary impact is spreading beyond petrol stations and into other goods and services, making the problem stickier. This faster-than-anticipated transmission forces a re-evaluation of the RBA's terminal rate. The bank now expects three more 25-basis-point hikes, taking the cash rate peak to 4.85%-a level not seen since late 2008. The market's initial expectation for a lower peak and earlier cuts is being reset by the reality of this oil shock.

The RBA's Expectation Gap: A Split Decision

The market's prior expectation for the RBA was a clean, predictable hike. The 25-basis-point increase to 4.1% was widely telegraphed. What wasn't priced in was the deep internal division that delivered it. The decision passed by a 5-4 vote, marking the narrowest split since the bank began disclosing votes. This isn't just a procedural note; it's a direct signal that the consensus view on the path ahead is fracturing.

The dominant market consensus had settled on a single May hike. The split vote directly challenges that narrative. As the RBA's own statement noted, the close call shows less agreement about what happens next. The Governor confirmed all members see further tightening as necessary, but opinions differed sharply on timing. This uncertainty suggests the widely held view of a May move may be too optimistic, especially if the oil shock proves more persistent than expected.

The hike itself resets the starting point for the tightening cycle. By raising rates back to where it was in February 2025, the RBA effectively wipes out the relief from two cuts delivered last year. This isn't a continuation of a trend; it's a reversal of recent policy easing. The expectation gap now isn't just about the oil price shock, but about the RBA's own internal debate on how aggressively to fight it. The split vote has opened the door to further hikes, but it has also introduced a new layer of volatility into the market's forward view.

Westpac's Revised Call: A Higher Terminal Rate

Westpac's forecast shift is a direct response to the oil shock's unexpected persistence. The bank now sees the RBA hiking in May, June, and August, lifting the cash rate peak to 4.85%. That's a clear move from its earlier guidance, which had pencilled in a lower peak and earlier cuts. This new path, a 17-year high, is the market's expectation gap closing in a painful way.

The bank's rationale hinges on two factors the market had underestimated. First, the supply disruption is longer than initially thought. Westpac's revised baseline assumes the Strait of Hormuz is effectively shut for around eight weeks, with a slow recovery in fuel supply thereafter. Second, and more critically, the inflationary impact is spreading faster than expected. The bank notes a rapid pass-through of higher fuel and oil-derived costs into other prices in Australia. This "second-round" effect means the shock is moving beyond petrol stations and into the broader economy.

Viewed through the lens of expectation arbitrage, Westpac is arguing that the RBA will be forced to tighten more aggressively than it otherwise would have to prevent these higher energy costs from becoming entrenched in inflation expectations. The bank believes the RBA will respond to this pricing behavior by tightening policy by more than would have been needed absent that pass-through. This is a classic guidance reset: the central bank's reaction function has changed because the economic reality has.

The implications for the forward path are severe. Westpac has pushed out the first rate cut to late 2027, with four cuts penciled in over 2028. This signals a prolonged period of higher rates, even after inflation finally cools. For the economy, the message is sobering. The higher cash rate profile will weigh on growth, with consumption in the firing line and a softer labour market ahead. Westpac now expects unemployment to peak near 5%. In short, the oil shock has not only raised the terminal rate but also extended the duration of the pain.

Catalysts and Risks: What Could Change the Script

The setup for Westpac's forecast is now clear: a prolonged oil shock is forcing a higher-for-longer rate path. The key variables that will determine if this script holds or if the market is overestimating the shock are the actual duration of the disruption and the RBA's reaction to it. The primary catalyst is the actual duration of the Strait of Hormuz closure and the pace of normalization. Westpac's baseline assumes the strait is shut for around eight weeks. A quicker reopening would drastically reduce the inflationary shock, potentially invalidating the need for three more hikes. Conversely, if the closure extends beyond that estimate, the pressure on inflation and the RBA's policy response would intensify.

A key risk is that the RBA's aggressive tightening overshoots, triggering a sharper-than-expected growth slowdown and forcing a premature pivot. Westpac's own analysis shows the higher cash rate profile will weigh on Australia's economic outlook, with slower growth and a softer labour market. The bank now expects unemployment to peak near 5%. If the economy weakens faster than the bank anticipates, the RBA could be forced to cut rates sooner than its current 2028 timeline, creating a volatile reversal for bond markets and mortgage holders.

The most critical near-term signal to watch is the persistence of second-round inflation pressures. Westpac's rapid pass-through assumption is central to its forecast. Monitor for signs that higher fuel costs are spreading into services and wages, which would validate the bank's view and justify further hikes. The recent surge in oil prices to their highest level in nearly two weeks amid deepening conflict suggests this pressure is building. However, the halving of fuel excise announced by the national cabinet provides a near-term offset for headline CPI, though it does not affect other oil-related products. This creates a tension: the tax cut may dampen immediate consumer pain, but the underlying cost pressures from plastics, aviation fuel, and damaged production facilities remain, as Westpac notes.

In essence, the market is pricing in a severe, persistent shock. The expectation gap will close based on two things: the real-world timeline for energy market normalization, and the RBA's assessment of whether inflation is becoming entrenched. Any deviation from Westpac's eight-week closure baseline or a faster-than-expected economic slowdown could reset expectations once again.