Why a diesel spike matters more than a petrol rise

Tuesday, 10 March 2026

Diesel prices have jumped more sharply than petrol over the past few days as conflict involving Iran has rattled global oil markets and put fresh pressure on the economy.

A comparison of Gaspy listings checked on Friday, March 6, and again on Tuesday, March 10, showed diesel rising by a lot more than petrol.

At Allied Wainoni, diesel rose from 164.9 cents a litre to 200.9c, a jump of 36c. Over the same period, 91 and 95 octane petrol rose by 16c.

While that will hurt the wallets of diesel car owners, this is more than a forecourt story.

Diesel matters differently from petrol because it keeps much of the productive economy moving. When it rises faster, the pressure lands first on freight, farming and working vehicles, then spreads more widely through supply chains and consumer prices.

New Zealand imports about 3700 million litres of diesel a year, compared with about 3000 million litres of petrol, underlining diesel’s importance to the wider economy.

AA principal policy adviser Terry Collins said diesel tends to attract a premium in times of global disruption because it is the fuel that keeps goods and much of the productive economy moving.

Petrol is used mainly by the light vehicle fleet. Diesel, by contrast, underpins road freight, farm machinery, harvesters and many commercial vehicles. That means when supply is under pressure, buyers are often willing to pay more to secure diesel because it is more critical to transport and production.

Collins said that dynamic was playing out internationally, not just in New Zealand.

“It’s a global thing that’s happening and they’re all reacting the same and all for the same reasons, which is basically they all want to make sure they’ve got enough to keep their economies going,” he said.

In other words, diesel is rising faster because, in a supply scare, markets treat it as the higher-priority fuel.

Also, there is no sign of a shortage and there are ships arriving from Singapore with fuel every second day.

Part of the difference is also structural. Petrol carries higher fixed taxes at the pump, while diesel users pay much of their road costs separately through road user charges, making diesel prices more directly exposed to swings in the underlying fuel market.

Under new rules that took effect this year, importers must hold minimum reserves in New Zealand or on ships heading here – at least 28 days of normal petrol demand, 21 days of diesel and 24 days of jet fuel. That stock is on top of fuel already sitting in service-station tanks.

Transporting New Zealand chief executive Dom Kalasih said in a statement that it mattered because diesel is one of the road freight sector’s biggest costs, meaning sustained increases can quickly put pressure on transport rates.

He said diesel was typically the industry’s second-largest cost after wages, and warned many operators had limited room to absorb higher prices.

“With around 93% of New Zealand’s freight moved by road, changes in diesel prices flow through the supply chain and can ultimately affect the cost of goods for businesses and consumers,” Kalasih said.

What happens next will depend on how long the disruption lasts and how global oil markets respond.

Collins said the current market was highly volatile, making it difficult to say whether the latest diesel jump would prove short-lived or stick for longer.

“The fundamental is that we’ve had a disruption to supply. And so that will mean that prices go up,” he said.

He said sharp swings in oil prices over recent days showed how uncertain the outlook remained. If supply concerns ease, diesel prices could settle back. But if the disruption continues, businesses and motorists may have to brace for more pressure at the pump.