Fuel Octane Rating: Premium vs. Regular Gas Explained

Ever pulled up to the pump and stared at the three fuel options-regular, mid-grade, premium-and wondered if spending extra on premium gas actually does anything? You’re not alone. Most drivers assume higher octane means better performance, better mileage, or a cleaner engine. But here’s the truth: for the vast majority of cars, premium gas is just a waste of money. And if you’re putting it in a car that doesn’t need it, you’re not helping your engine-you’re just paying more at the pump.

What Does Octane Rating Even Mean?

Octane rating isn’t about how much energy is in the fuel. It’s not a measure of quality or cleanliness. It’s a number that tells you how resistant the fuel is to premature ignition-something called engine knock.

Engine knock happens when the air-fuel mixture in your cylinder ignites before the spark plug fires. This can occur under high pressure and heat, especially in engines with high compression ratios. Instead of burning smoothly, the fuel explodes in random spots, creating a knocking or pinging sound. Over time, this can damage pistons, valves, and cylinder walls.

Higher octane fuel resists this premature ignition better. That’s why high-performance engines-like those in sports cars or turbocharged models-need it. They squeeze more air and fuel into the cylinder, creating more heat and pressure. Without high-octane fuel, they’d knock themselves apart.

Regular vs. Premium: What’s the Difference?

In the UK and most of Europe, you’ll typically see three grades:

• Regular (RON 95) - The standard fuel for most cars. RON stands for Research Octane Number.
• Mid-grade (RON 97) - Less common, sometimes called "super" or "plus".
• Premium (RON 98 or 99) - Often branded as "Ultimate", "V-Power", or "Premier".

The difference between RON 95 and RON 98 isn’t huge in terms of energy content. Premium fuel doesn’t have more power-it just burns more slowly and evenly under pressure. That’s it.

Most modern cars run perfectly fine on RON 95. In fact, over 90% of vehicles on UK roads are designed to use it. The engine control unit (ECU) adjusts timing automatically to prevent knock, even with regular fuel. So unless your car’s manual says otherwise, you’re not doing your engine any favors by upgrading.

When Do You Actually Need Premium Gas?

You only need premium fuel if your car’s manufacturer specifically recommends it. Check your owner’s manual. Look for phrases like:

• "Requires premium unleaded fuel"
• "Premium fuel recommended for optimal performance"
• "Use 98 RON or higher"

If it says "recommended," you can usually use regular without damage. If it says "required," then stick with premium. Skipping it in a high-performance engine can cause knocking, reduced power, and even long-term damage.

Common models that need premium fuel include:

• BMW 3 Series (turbocharged models)
• Audi S-line and RS models
• Volvo T5 and T6 engines
• Subaru WRX and STI
• Many newer Mercedes-Benz and Porsche models

These engines have high compression ratios or turbochargers that create more heat and pressure. They’re built to run on higher octane. Using regular fuel here isn’t a gamble-it’s a risk.

Does Premium Gas Improve Fuel Economy?

Here’s the myth: premium gas gives you better mileage. The reality? Almost never.

In a car designed for regular fuel, premium gas won’t improve your miles per gallon. The engine doesn’t know how to use the extra octane. It runs the same way regardless. You’re paying 10-15% more for no gain.

In a car that requires premium, you might see a slight improvement in efficiency-maybe 1-2%-because the engine can run at its optimal timing. But that tiny gain rarely pays back the extra cost. For example, if premium costs £1.45 per litre and regular is £1.30, and you get 35 miles per gallon on both, you’d need to drive over 2,000 miles to break even on the price difference. And that’s assuming perfect conditions.

Real-world tests by the AA and consumer groups in the UK show no consistent fuel economy benefit from premium gas in cars that don’t require it.

What About Engine Cleaning?

Some brands claim their premium fuels have better detergent additives that keep engines clean. That’s partly true-but not because of the octane.

All fuels sold in the UK must meet minimum detergent standards set by the government. The difference between brands is in the additive packages, not the octane level. A regular-grade fuel from Shell V-Power Nitro+ might have more cleaning agents than a premium-grade fuel from a lesser-known brand.

If you’re worried about carbon buildup, use a fuel system cleaner every 15,000 miles. Or choose a brand known for quality additives, regardless of octane. Brands like Shell, BP, and Total all offer good detergents in their regular grades.

What Happens If You Use the Wrong Fuel?

Accidentally putting premium in a car that takes regular? No problem. You’re fine.

Putting regular in a car that needs premium? That’s where trouble starts.

Modern cars have knock sensors. If they detect pinging, they’ll pull back ignition timing to protect the engine. That means less power, worse acceleration, and slightly lower fuel economy. You might notice your car feels sluggish, especially when overtaking or climbing hills.

Long-term use of low-octane fuel in a high-compression engine can lead to carbon deposits, overheating, and even piston damage. It’s rare, but it happens-especially in older turbocharged engines or if you frequently drive hard.

If you’ve accidentally used regular in a premium-required car, don’t panic. Fill up with the right fuel next time. One tank of regular won’t break your engine. But don’t make it a habit.

Is Premium Gas Worth It for Older Cars?

Many classic car owners think premium is better for older engines. That’s a misunderstanding.

Older cars (pre-1990s) were designed for leaded fuel, which had high octane and protected valves. Modern unleaded fuel doesn’t have lead, so some classic cars need lead additives or hardened valve seats to prevent damage.

But octane isn’t the issue. If your classic car knocks on regular fuel, it’s because of the lack of lead, not because the octane is too low. You need an additive like Castrol Valvemaster, not premium fuel. In fact, many classic cars run fine on RON 95.

Check your owner’s manual or consult a classic car specialist. Don’t assume premium = better for vintage engines.

Bottom Line: What Should You Do?

Here’s your simple guide:

1. Check your owner’s manual. If it says "premium required," use RON 98 or higher.
2. If it says "premium recommended," you can use regular without harm. Premium might give you a tiny bit more power, but not enough to justify the cost.
3. If it says "regular unleaded," stick with RON 95. Premium won’t help.
4. Don’t fall for marketing claims about cleaning, mileage, or engine life. Those are unrelated to octane.
5. If you hear knocking, switch to higher octane immediately. That’s your engine telling you it’s in danger.

Spending extra on premium gas is like buying designer running shoes for a walk to the shops. It doesn’t make you faster. It just costs more.

Save your money. Use the fuel your car actually needs. Your wallet-and your engine-will thank you.