What the octane number actually measures
The number on the pump — 93 or 95 — is not a measure of power, energy, or how "clean" the fuel is. It measures one thing: the fuel's resistance to igniting under pressure before the spark plug fires. That premature ignition is called knock (or pinking), and it's what the octane rating exists to prevent.
A higher octane number means the fuel can be squeezed harder inside the cylinder before it self-ignites. That's it. Two litres of 93 and two litres of 95 from the same brand contain almost identical energy and will take you almost exactly the same distance. The 95 is simply harder to make knock.
Why the coast only sells 95 — and the highveld sells both
This is the part most drivers never had explained to them. It comes down to altitude, not quality.
Air gets thinner the higher you go. Johannesburg sits around 1,750m above sea level; Cape Town and Durban are essentially at sea level. Thinner highveld air means less oxygen packed into each cylinder, which means lower pressure during compression — and lower pressure means the fuel is far less likely to knock. So inland, 93 octane is perfectly adequate for most engines, and it's sold alongside 95.
At the coast, dense sea-level air produces higher cylinder pressure, so engines are more prone to knock. To give every car enough margin, coastal regions standardise on 95 and simply don't sell 93. You're not paying for a premium — it's the baseline grade for where you are.
If you buy a car in Gauteng that's only ever run on 93 and move to Cape Town, nothing breaks — you just fill up with 95 from then on, and your car will run slightly better if anything. The reverse is fine too: a coastal car run on 93 inland will adapt. Modern engines manage this automatically.
How to find the octane your car was built for
You don't have to guess, and you shouldn't rely on what the previous owner used. The manufacturer specifies a minimum octane, and there are two places to find it:
- The fuel filler flap. Open the petrol cap and look at the inside of the flap. Many cars have a small sticker stating the minimum octane — for example "Unleaded 95 RON" or "95 recommended, 93 minimum".
- The owner's manual. Look under "fuel" or "specifications". This is the definitive source and will state the minimum required and the recommended grade.
Most ordinary petrol cars in SA are happy on 93 inland and 95 at the coast. The cars that genuinely need 95 — or even insist on it — are turbocharged engines, high-compression performance models, and many modern direct-injection engines. If you're inland and your manual says 95 is required, take that seriously rather than saving a few rand on 93.
| Your car type | What to use inland | At the coast |
|---|---|---|
| Ordinary petrol engine, no turbo | 93 is fine; 95 won't hurt | 95 (only option) |
| Turbo or high-compression engine | 95 — check the manual | 95 |
| Performance car requiring 95+ | 95 always | 95 |
| Diesel | Octane doesn't apply — diesel uses a separate cetane rating | |
The "higher octane = more power" myth
This is the single most common misunderstanding at the pump. Pouring 95 into a car designed for 93 does not give you more power, better economy, or a cleaner engine. The engine can only use the octane it was tuned for — the extra knock resistance simply goes unused. You're spending more for no benefit.
"95 is the premium fuel, so it must be better for my car." Octane is not a quality grade. A normal engine designed for 93 gains nothing from 95. The only cars that benefit are those the manufacturer designed to need it.
The detergent additives that genuinely keep an engine clean are a separate thing entirely. Premium branded fuels (the V-Power and similar lines) add extra cleaning agents — but that's the brand's additive package, not the octane number doing the work.
Can you run 93 in a car that recommends 95?
For most modern cars, yes — within reason, and inland. Almost every fuel-injected car built in the last 25 years has a knock sensor. If it detects knock on a lower octane, it automatically retards the ignition timing to protect the engine. The trade-off is slightly less power and slightly worse economy, but no damage.
Where you should not cut corners is a car that requires (not just recommends) 95, or an older performance engine without a knock sensor. Persistent knock in an unprotected engine causes real, expensive damage over time. When the manual says "minimum 95", that word is the line.
What this means when you're buying a used car
Octane rarely shows up as a tick-box on an inspection, but it matters to your running costs and it can flag a mismatch worth a question:
- Buying a turbo or performance car inland? It will need 95, which is the pricier grade. Build that into your monthly fuel budget before you commit.
- Listen for knock on the test drive. A light metallic rattle under hard acceleration — especially uphill or pulling away — can point to the wrong fuel, but also to carbon build-up or timing issues. Our Test Drive inspection section covers what to listen for.
- A coastal car moving inland (or vice versa) is not a red flag. Fuel grade is never a reason to avoid an out-of-province car — the engine adapts to whatever you put in.
Use what the manual says — nothing more, nothing less
Inland, ordinary cars run perfectly on 93 and gain nothing from 95. At the coast, 95 is your only choice and that's fine. The cars that truly need 95 will say so on the fuel flap or in the manual — and those are the ones to never compromise on. Everyone else is free to stop paying the "premium" myth tax.
Frequently asked questions
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Get the Complete Inspection Guide Bundle — R299 →This guide is general information for South African motorists, not official confirmation. Fuel prices are set monthly by the Department of Mineral Resources and Energy (DMRE) and differ by fuel zone. Always confirm the current price at the pump or via the DMRE's official schedule before budgeting.