What is Brent crude?
Brent crude is the global benchmark price for oil, set daily on international commodity markets. Australia imports roughly 70% of its refined petrol — all of it priced off Brent. When Brent moves, Australian pump prices follow.
Why is there a lag between the two lines?
Refineries buy crude oil weeks in advance. The fuel you pump today was purchased as raw crude 2–4 weeks ago. This creates a predictable delay: Brent rises or falls first, and bowser prices adjust 10–28 days later as pre-purchased stock is consumed and new, pricier crude enters the supply chain.
The "rockets and feathers" effect
ACCC research consistently shows Australian pump prices rise faster when crude goes up ("rockets") than they fall when crude comes down ("feathers"). Retailers pass on cost increases quickly but are slower to pass on savings. The wider the gap between the two lines after a Brent fall, the more pressure on retailers to cut prices.
What the shaded gap tells you
The vertical distance between the Brent line and the petrol line — after accounting for both axes — represents the transmission lag. When Brent is rising steeply but petrol hasn't fully caught up, further pump price rises are likely incoming. When Brent has eased but petrol remains elevated, consumers are being overcharged relative to crude costs.
War context: Strait of Hormuz
Roughly 20% of global oil supply passes through the Strait of Hormuz daily. The 2026 Iran war directly threatens this chokepoint. Every credible threat to Hormuz shipping adds a risk premium to Brent, which flows through to every Australian petrol station within weeks — regardless of whether a tanker is actually stopped.