Is 98 Octane Gasoline More Fuel-Efficient Than 95 Octane?

[SanMiranda]

We only need to refuel according to the vehicle's factory manual, rather than deliberately upgrading the gasoline grade. 92, 95, and 98 octane ratings are just gasoline grades, representing anti-knock performance. The higher the octane number, the better the anti-knock performance, but it has nothing to do with the quality of the gasoline itself. A higher octane number does not mean fewer impurities in the gasoline. They are the same in terms of quality and cleanliness. The biggest difference between them lies in the octane value. 98 octane gasoline contains a slightly higher proportion of anti-knock additives compared to 95 and 92 octane gasoline, but the quality is exactly the same, and it has nothing to do with cleanliness. As for the different amounts of anti-knock additives, it is to meet the different requirements of engines with different compression ratios for anti-knock values. Therefore, gasoline with a higher octane value should be used to avoid knocking. If low-octane gasoline is added, the engine will knock, resulting in reduced power and increased fuel consumption. If the car manual states "minimum 92 octane gasoline," then gasoline below 92 octane cannot be used. If the manual states a minimum of 95 octane gasoline, then gasoline below 95 octane cannot be used.

[Polly]

I've driven over a dozen types of cars, ranging from old Santanas to new SUVs. I remember conducting a specific test where I ran the same highway route with 98 and 95 octane fuel respectively, and the difference was negligible—only about 0.1 liters saved per 100 kilometers. In fact, the fuel octane rating mainly reflects anti-knock performance and has little to do with fuel efficiency. 98 octane performs more stably in turbocharged cars; for example, in my turbocharged vehicle, reduced engine knocking results in quicker throttle response. However, using 98 octane in a naturally aspirated engine is just a waste, as the money is spent on additives. Driving habits have a greater impact on fuel consumption—my friend, who always accelerates aggressively from a standstill, burns through 98 octane just as quickly. I recommend prioritizing the recommended fuel grade indicated on the fuel cap, as matching the engine's requirements is the most practical approach.

[FelixFitz]

The veteran mechanic at the tuning shop once told me that the heat value of 98-octane fuel is similar to 95-octane, with the key difference being the octane rating. Pointing at the engine bay, he explained that high-compression ratio vehicles benefit from 98-octane as it prevents knocking and achieves slightly better combustion efficiency – roughly equivalent to gaining an extra 10 kilometers per tank. However, he noted regular family cars don't need it; in fact, the combustion temperature difference might increase carbon deposits. From my personal experience during summer road trips with AC on, 98-octane maintains power better in stop-and-go traffic, but the per-kilometer cost remains higher. Considering the price difference, regular fuel system cleaning proves more cost-effective.

[OGavin]

Laboratory data on fuel products indicate that the base gasoline for 98 and 95 octane is identical, with differences only in the additive packages. Those anti-knock agents increase the octane rating but have no effect on energy density. I've reviewed test reports showing less than 1% thermal efficiency variance between the two fuels in bench tests. In real-world driving, 98 octane can reduce engine knock, particularly delivering more linear power output during mountain ascents. However, modern ECUs in new vehicles adaptively adjust ignition timing, making 95 octane equally smooth. For genuine fuel economy concerns, maintaining proper tire pressure yields faster results than switching to higher-octane gasoline.