Which Petrol Should I Use?

What kinds of petrol are there?

The numbers are the most relevant. Standard unleaded petrol is 91. This is sort of the stock standard for many cars. Premium unleaded is both 95 and 98. The ethanol-blended e10 (a mixture of up to 10% ethanol in petrol) is a fuel that can be used as a substitute for 91 in most cars.

Those numbers – 91, 95 and 98 – encompass the octane rating of the fuel. They’re all about the same in terms of the energy in the fuel. Really octane is a measure of how much heat and pressure a fuel can withstand before igniting. 

Manufacturers design engines for a minimum octane rating. If you open the fuel flap of your car and it says “unleaded petrol only” it means 91 octane fuel is okay to use. If it says “premium unleaded only” it means you need to use at least 95. And if the fuel flap tells you to use 98, you use 98.

Can I put a higher octane fuel in my car?

It won’t hurt your engine if you use a higher octane fuel. For example, if you use 95 or 98 in an engine designed for 91, that’s fine. However, avoid using a lower octane fuel than the minimum recommended by the manufacturer. Using 91 in an engine designed for 95 or 98 is potentially destructive.

High-octane petrol, often labelled premium or supreme, sounds as if it should rank mightily above plain old regular. Fuel retailers say that it improves overall performance and engine efficiency. Retailers aren’t lying, but they do sometimes overstate the benefits. Most engines will adapt very slightly if you run them on a higher octane fuel than the minimum recommended. 

But in practice, the improvement is small, and the price premium of the higher octane fuel always eclipses the economic benefit from running it. In other words, it’s not an economically rational choice to run 98 in an engine designed for 91, even though it might run slightly better. The small increase in fuel economy isn’t enough to overcome the extra cost. A premium tag doesn’t mean the fuel is of better quality either. As all petrol sold in New Zealand has to meet strict quality levels.

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The reality

While it might appear that using a higher octane petrol than specified for your vehicle might unleash some hidden power within your engine, you’re not really doing anything for it. Most cars in NZ are designed to run on 91 octane fuel.

So, just use what your car is designed for and you’ll be fine.

What about e10?

Ethanol is an octane booster and can enhance performance, but the slight negative is there can be around a 3% increase in fuel consumption. It isn’t a substitute for premium unleaded petrol. If your car requires 95 or 98, e10 is not a viable fuel for it. The majority of cars on New Zealand roads designed for 91 petrol can accept e10 – but you should check the owner’s manual or ask the manufacturer or dealer first.

What’s the word on fuel prices?

Petrol prices rose overnight in July, as the government’s fuel tax discount came to an end: July 1 saw petrol prices increase by 25c, and GST by nearly 4c. And, unfortunately, it doesn’t appear fuels costs will come down any time soon.

Despite the hike in prices, fuel is still about 40c cheaper than it was at its peak last year, just after Russia’s invasion of Ukraine led to a spike in global fuel rates.

But even disregarding fuel price fluctuations due to global conflict, a market study conducted by the Commerce Commission last year found motorists are still paying more than they should for petrol. The report found fuel companies are making high profits due to a lack of competition in the industry.

Following the report, the government introduced the Fuel Industry Bill. It aims to introduce changes it says will promote greater competition in the fuel market at the wholesale level, ideally leading to lower prices for motorists. Their focus on making changes at the wholesale level are intended to grant smaller players, such as Waitomo and Gull, access to cheaper fuel.

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About the author of this page

This report was written by Canstar Content Producer, Caitlin Bingham. Caitlin is an experienced writer whose passion for creativity led her to study communication and journalism. She began her career freelancing as a Search Engine Optimiser, before joining the Canstar team.