Is it worthwhile spending the extra money on premium fuel?

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There has been something of a propaganda campaign to try to convince motorists that premium fuel burns cleaner and results in better fuel consumption figures, but is it true?

Premium fuel has a higher octane rating than standard unleaded. Normal unleaded is rated at 91 octane. Depending on where you buy your fuel, you can fill up with 95 octane or ultra-premium at 98 octane.

Of course, we are all susceptible to numbers and inclined to think higher equals better.

The internal combustion engine works on the principle of drawing in fuel and air on the downstroke (intake), squeezing it on the upstroke (compression) and then igniting it (the power stroke), which in turn pushes the piston back down and turns the crankshaft. On the next upstroke, the remaining gases are pushed out of the engine through the exhaust. And that’s why it’s called a ‘four-stroke’ engine.

The higher the compression on the upstroke, the more force is generated and applied to the downstroke. That’s why so-called high compression engines are more powerful.

If the remnants of gases from the previous ignition stroke cause the fuel/air mixture to ignite before the piston reaches its highest point in the engine, it’s called a misfire and the noises it produces are known as ‘knock’. The result is a loss of power.

The solution is to retard the explosion, so that it happens at just the right moment. Premium fuel is just as explosive as lower octane fuel, but doesn’t ignite as soon.

91, 95 or 98?
Those old enough to remember will recall that low quality fuel made high compression engines impractical. Way back, those of us using high performance engines had to find and use av (aviation) gas (usually rated at 100 octane) to get the best performance out of our engines. Using a lower octane fuel caused the dreaded ‘knock’, in turn leading to premature engine wear and fouled spark plugs.

Modern cars use a variety of sensors to adjust the engine timing to compensate for different octane ratings. If your owner’s manual recommends 95 or 98 octane fuel, these electronics will usually eliminate knocking if you occasionally have to fill with a lower-than-recommended octane fuel, but doing it consistently isn’t a wise policy.

Premium fuel, as the name implies, costs more than non-premium fuel, and often by a considerable margin. If your car is recommended to run on 91 octane fuel, filling it with premium won’t do any harm, but it will add considerably to your running costs.

Despite claims you may have heard, premium fuel does not clean your engine. The additives in some fuels are designed to clean older engines but won’t make much difference to cars with modern fuel-injection systems.

Also, you may notice a small improvement in fuel consumption but nowhere near enough to offset the higher cost. You’ll see far better results by adopting economical driving habits, keeping your car tuned and ensuring your tyres are at the recommended pressure.

Do you buy premium fuel? Are you sure it is worth the extra money?

Paul Murrell is a motoring writer and creator of, which specialises in “car advice for people whose age and IQ are both over 50”. This article first appeared on

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Total Comments: 7
  1. 0

    “The higher the compression on the upstroke, the more force is generated and applied to the downstroke.”
    A rather simplistic and inaccurate “fact”… if it was true, there’s be a lot more mighty fast diesels about, given they have higher compression than petrol engines.
    All other things being equal, the higher the upstroke compression the more it will slow down the piston, downstroke inertia, and engine RPM.
    The reason high compression petrol engines tend to have greater power output is the more air that is being compressed, the more oxygen is in that air, which means more fuel can be added while still getting a good (stoichiometric) fuel/ air ration (about 14/1). More air and more fuel = more bang.

    The writer’s bottom line is fine, the above reasoning not so fine.

  2. 0

    I’ve read many articles on this and the advice of experts is always the same. Use whatever your car is designed to run on. If your car is designed to run on standard unleaded then use it because premium adds nothing other than cost. I rented a Hyundai Elantra in Canada last year. It is designed to run on 87 octane and did so perfectly. European cars almost always require premium 95 which at $7 to $8 extra per tank fill is something to consider when buying a car.

  3. 0

    Years ago a test at a disused airfield had the same car filled with lowest (cheapest) octane fuel and then driven at a constant speed until the rule ran out. The test was repeated for the next higher octane fuel, and then repeated with the highest octane rating (most expensive fuel). The results showed the highest octane caused the car to travel furthest, the middle octane caused the middle distance, and the lowest octane caused the least distance. However, when the distances were divided into the cost of each tank full the result was that all three fuels produced the same cents per kilometre.

    Hence I fill with the most expensive as it costs the same per kilometre, but requires filling less often.

  4. 0

    As I have said before use the best fuel you can afford, keeps engine and bits claener and is better for power, if extra power is not used its a lot cheaper in the long run, its not hard to test for yourself.
    DO NOT USE E10, biggest rip off, not cheaper to run, you use more fuel for the same kilometres and it is not cost effective, it is also hydroscopic, it absorbs water which is not good if you are locked down or not using the car for long trips, Short trips will kill your car.
    It damages fuel systems, the government is mandating servos SELL E10 but most servos tell me its hard to sell if people don’t want it. The government is getting paid under the table by the manufacturers on pretext of employment and polution to use this rubbish.
    I cannot repeat this enough, DO NOT USE E10.



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