Premium petrol - should you buy it?

For most motorists there's no reason to splash out for premium. Here's why you're probably fine sticking with 91.

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Premium, Supreme, Ultimate. Higher-octane petrol certainly sounds much more exciting than plain old “regular”. It also comes gushing with claims. According to fuel companies, it “cleans vital engine parts” and “improves engine efficiency and overall performance”. So should we all be using premium petrol?

For most motorists, no. Using premium 95 or 98 petrol offers only marginal benefits over regular 91. The “premium” tag doesn’t mean the fuel is better quality, as all petrol sold in New Zealand has to meet stringent quality levels.

What's the difference?

The octane rating of petrol (91, 95 or 98 in New Zealand) signifies its ability to resist detonation. An engine is tuned to use petrol of a certain octane. In the engine, petrol is compressed by a piston, then ignited by a spark. The resulting explosion pushes the piston down. If the petrol detonates too early, which can happen when using a lower-octane fuel than the engine needs, it can try to force the piston down before it has reached the top of its stroke. This is noticeable as a “knocking” sound in your engine and can cause serious damage if left unchecked.

Most car engines are designed for regular 91 octane petrol. Japanese cars usually use regular 91 petrol as that fuel is widely available in Japan. But some exceptions in New Zealand need premium 95 octane petrol. These include older models and many European-designed cars (the lowest octane fuel readily available in Europe is 95). While modern cars that need premium petrol can tolerate some use of regular 91, long-term use of a lower octane could damage the engine.

What about those claims?

Using higher-octane fuel in a car that isn’t designed for it is unlikely to result in improved performance or fuel efficiency.

Some manufacturers claim their particular mix of premium additives makes a difference. For example, Z Energy says its ZX Premium 95 octane petrol (with a “friction modifier”) returned 3% better efficiency than another 95 octane fuel in its testing.

All fuel brands claim the additives in their premium petrol clean your engine, resulting in vague claims of “improved engine efficiency and performance over time” (Caltex).

However, these types of claims regularly come with disclaimers, such as “benefits are based on drive cycles in a laboratory and may not reflect real-world driving results” (BP). As they are practically impossible to verify, we’d question their value to motorists.

Pricey choice

Premium petrol comes at a price. In a review of 11 service stations (5 brands) in Wellington on 27 January, premium 95 (sold at 9 locations) was 7 to 11c per litre more than regular 91. Premium 98 petrol was 17c per litre more than regular 91 at the one service station offering it.

Most service stations don’t show their premium petrol prices on a prominent roadside board. At the 11 service stations we visited in Wellington, just 1 (Caltex) displayed its premium petrol price on a roadside board. That means you won’t know the cost of premium petrol until you drive up to the pump.

Not all garages sell all premium grades. Gull only sell 91 and 98 octane and while BP has 95 in the North Island, it has only limited availability in the South Island. So depending where you fill, you may be stung for the extra cost of 98 petrol.

Our advice

Use the lowest octane your car needs — for the majority of motorists, that’ll be regular 91. If you are unsure, check your manual. It might also have a sticker inside the fuel flap. You could also ask your car manufacturer or at a dealer for the brand.

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John S.
03 Jan 2018
My manual Ford Focus (10yr old, bought new) pinks like hell on 91 but 95/98 is overpriced ...

3.1.2018. We have been housesitting around the north island for 18 months and so our car is often fully loaded with suitcases and stuff - uphill and downdale - now have 110,000kms on the clock. I stopped using 91 because of the pinking and poor hill power. However, the petrol costs have shot up - we used to see a premium of about 8-10c on 95/98, but now it is often more like 15 to 25c. As there are about 20% of cars needing higher octane fuel, us users must be paying in part for the 91 octane discounts required by the government/supermarket incentives - hardly fair IMHO.

Anthony H.
06 Jun 2017
Article based on no actual testing

Your statement of "most motorists would get marginal benefits using higher higher octane " is a claim based on no actual research or data that you have supplied. .Poor article.

Shona M.
04 Mar 2017
1996 Corolla Wagon

My wagon has done nearly 300,000kms. It burns some oil and overall it's a pretty tired vehicle. The engine has a bit of a "rattle" which becomes noticeably worse if I fill up with the lower grade fuels. Therefore I always use 98. I guess a cheaper option would be to just turn my radio up louder :)

Dean J.
18 Feb 2017
98 Did Improve Economy

Our '99 Subaru Lancaster required super. We tried 98 and found we seemed to consistently get slightly better economy than 95 and 91. The latter was the odd "get you home" refill in rural SI. Not scientific based tests as the car isn't used in identical conditions from tank to tank.

We put it down to better engine response to the throttle and we needed less accelerator for similar performance.

John C.
18 Feb 2017
There IS a difference in performance!

Both my year old motorcycle and my late model Japanese car are recommended (in their respective manuals) to run 95. I once had to fill my motorcycle up with 98 octane and it most DEFINITELY ran smoother and felt more powerful (and it's a performance bike already!). However, by preference, I will run 95 in both vehicle, because of the cost of 98.

D & C M.
18 Feb 2017
Premium Petrol should you buy it

BP in the South Island does not sell the 95 octane fuel my car requires,therefore I have not been near BP for anything for years!