The golden rule: use what your car needs
The single most important thing about choosing fuel is that your car has a minimum requirement set by the manufacturer, and using a higher grade than it needs rarely gives you anything back. Buying 98 for a car designed to run on 91 mostly just costs more. The right question is not "which fuel is best?" but "what does my car actually require?"
You will find the answer inside the fuel filler flap, in the owner's manual, or often on the fuel cap itself. It will state a minimum octane (RON) or say the car is a diesel. Match that, and you are done — spending more delivers little to no benefit for most everyday vehicles.
The petrol grades explained
- Unleaded 91
- Standard regular unleaded, 91 RON. The default for most older and many current petrol cars that do not specify higher octane.
- E10
- Unleaded blended with up to 10% ethanol, with an octane rating around 94. Usually the cheapest option and fine for most cars made in recent decades, but check compatibility.
- Premium 95
- 95 RON premium unleaded, required by some vehicles and recommended for others. Only worth buying if your car specifies it.
- Premium 98
- 98 RON premium unleaded, the highest common octane. Needed by some performance and European engines; wasteful for cars designed for 91.
E10: cheaper, but check compatibility
E10 is petrol blended with up to ten per cent ethanol. It is usually a few cents a litre cheaper than 91 and has a slightly higher octane rating of around 94. For most cars built in the last couple of decades it is perfectly fine, and using it is an easy way to trim fuel costs.
The catch is that some older vehicles and a few specific models are not designed for ethanol blends, where it can affect fuel-system components. Check your manual or the manufacturer's E10 compatibility guidance before switching. Ethanol also has slightly less energy per litre than pure petrol, so you may see marginally higher consumption, though the lower price usually still comes out ahead.
Diesel and when premium is worth it
Diesel is a different fuel for different engines — you cannot put diesel in a petrol car or petrol in a diesel without serious damage. Diesel engines are common in utes, four-wheel drives and many European cars, and tend to offer better fuel economy and torque for towing and highway driving. If your car is a diesel, that is simply what it takes; the choice is which brand and whether premium diesel is worth it, which for most drivers it is not.
Premium petrol (95 or 98) is genuinely worth it only when your car specifies it as a minimum, or recommends it and you notice a real difference. For a car that requires 91, premium will not make it faster or cleaner in any way you will feel. Using a live fuel map to find the cheapest station for the grade your car actually needs — whether that is E10, 91 or diesel — saves far more than switching grades ever will. EnergySorted's map lets you filter by fuel type so you compare like with like.