What is the difference between regular gas and premium gas?

The difference is the octane rating, with regular gas at 87 and premium gas typically at 91 to 93, which measures the fuel's resistance to engine knocking.

Which is better, regular gas or premium gas?

Neither is universally better; premium gas is better only for engines that require it, while regular gas is better for engines designed to run on lower octane.

Is premium gas worth the extra cost?

No, premium gas is not worth the extra cost for vehicles that only require regular gas, because it provides no measurable performance or fuel economy benefit in those engines.

Can I use regular gas instead of premium gas?

Yes, you can use regular gas instead of premium gas only in an emergency, but doing so consistently in a required engine risks knocking, reduced power, and potential long-term damage.

What happens if I accidentally put regular gas in a premium car?

If you accidentally put regular gas in a premium car, the engine's knock sensors will adjust timing to prevent damage, but you may notice reduced power and lower fuel economy.

Does premium gas give better gas mileage than regular gas?

No, premium gas does not give better gas mileage than regular gas in an engine designed for regular, because octane rating does not affect fuel energy content.

How do I know if my car needs premium gas?

You know your car needs premium gas if the owner's manual or the fuel filler door explicitly states "premium fuel required," not merely "recommended."

Is it safe to mix regular gas and premium gas in the same tank?

Yes, it is safe to mix regular gas and premium gas in the same tank, because the blend simply results in an intermediate octane rating that is generally harmless.

Can I switch back and forth between regular and premium gas?

Yes, you can switch back and forth between regular and premium gas, because modern engines adapt to the octane level, provided you use premium when the manual requires it.

Why do some cars require premium gas while others use regular gas?

Some cars require premium gas because they have high-compression or turbocharged engines that need higher octane to prevent pre-ignition and knocking under load.

Difference Between

Difference Between Regular Gas and Premium Gas

Written byNex Virox Team

Editorial Team

Reviewed byVarshal Nirbhavane

Senior SEO & Organic Growth Professional · 5+ years

Published: August 27, 202619 min read

Quick answer

The main difference between Regular Gas and Premium Gas is their octane rating, which measures fuel’s resistance to engine knocking. Regular Gas is lower-octane fuel (87) for standard engines, while Premium Gas is higher-octane fuel (91–93) for high-performance or turbocharged engines.

Key takeaways

Core distinction: Regular gas has 87 octane, while premium gas typically has 91 to 93 octane.
How they work: Higher octane resists pre-ignition, allowing high-compression engines to run safely without knocking.
Cost and performance: Premium costs 20 to 40 cents more per gallon but adds zero power to standard engines.
Best-fit use: Use premium only when your owner's manual requires it, such as turbocharged or luxury vehicles.
Common mistake: Many drivers waste money on premium because they believe it cleans engines or boosts fuel economy.

Table of Contents18 sections

Difference Between Regular Gas and Premium Gas: Comparison Table

Aspect	Regular Gas	Premium Gas
Definition	Standard unleaded fuel with an octane rating of 87 in the US and Canada.	Higher-octane unleaded fuel typically rated at 91, 93, or 94 in North America.
Purpose	Fuels most everyday commuter engines designed for standard compression ratios.	Prevents knock in high-performance and turbocharged engines with high compression.
Core Mechanism	Resists pre-ignition at lower compression pressures found in standard engine designs.	Resists spontaneous combustion under higher cylinder pressures and temperatures before the spark fires.
Octane Rating	Rated at 87 (AKI) in the US and 91-92 RON in Europe.	Rated at 91-93 (AKI) in the US and 95-98 RON in Europe.
Compression Ratio	Suits engines with compression ratios typically below 10.5:1.	Required for engines with compression ratios above 10.5:1 to avoid detonation.
Engine Compatibility	Safe for engines whose manufacturer explicitly recommends 87 octane fuel.	Mandatory only in engines whose owner's manual states premium is required.
Turbocharged Engines	Can cause knock in forced-induction engines that demand higher octane under boost.	Prevents detonation when turbochargers compress air and raise cylinder temperatures.
Performance Output	Delivers rated horsepower only in engines calibrated for 87 octane fuel.	Unlocks full rated horsepower in engines whose ECU advances timing for high octane.
Fuel Economy	May improve mileage slightly in engines tuned for regular because timing stays optimal.	Offers no measurable mileage gain in engines not calibrated to advance timing for it.
Energy Content	Contains roughly the same energy per gallon as premium, about 114,000 BTU.	Holds no more energy per gallon than regular despite its higher octane rating.
Price Per Gallon	Costs less, typically 20 to 50 cents cheaper per gallon than premium in the US.	Costs more, typically 20 to 50 cents more per gallon than regular at US pumps.
Detergents	Contains Top Tier detergents only if the station meets that certification standard.	Often carries the same detergent levels as regular, not automatically higher quality.
Knock Resistance	Burns with lower resistance to pre-ignition under heavy load or high heat.	Withstands higher cylinder pressure before the air-fuel mixture self-ignites.
Ignition Timing	Forces the engine control unit to retard timing if knock sensors detect detonation.	Allows the ECU to advance spark timing closer to the ideal for maximum torque.
Carbon Deposits	Leaves deposits at similar rates to premium when both meet the same detergent standard.	Does not inherently clean engines better unless it meets the Top Tier detergent spec.
Engine Longevity	Preserves engine life when used in engines designed and calibrated for 87 octane.	Prevents long-term knock damage in engines that require it for safe operation.
Knock Sensors	Relies on knock sensors to detect detonation and retard timing as a safety measure.	Gives knock sensors less work because the fuel itself resists premature ignition.
Warranty Compliance	Maintains manufacturer warranty only when the manual lists 87 octane as acceptable.	Required to keep the powertrain warranty valid on vehicles that mandate premium fuel.
High Altitude	Works well at altitude where thinner air naturally reduces effective compression pressure.	Provides no extra benefit at altitude because lower air density already suppresses knock.
Cold Weather	Starts easily in cold temperatures due to its volatility matching standard winter blends.	Starts equally well in cold weather, showing no advantage over regular in freezing climates.
Hot Weather	Risks knock more readily in extreme heat when intake air temperatures rise sharply.	Maintains knock resistance better during hot weather, heavy loads, or towing.
E85 Flex Fuel	Cannot be substituted with E85 in vehicles not explicitly designed as flex-fuel.	Cannot be substituted with E85 unless the vehicle is a certified flex-fuel model.
Diesel Engines	Never used in diesel engines, which require compression-ignition diesel fuel.	Never used in diesel engines, which require diesel fuel, not spark-ignition gasoline.
Availability	Offered at nearly every gas station worldwide as the default pump grade.	Available at most stations but sometimes missing at smaller rural or discount outlets.
Common Vehicles	Powers most sedans, SUVs, and trucks like the Toyota Camry and Honda CR-V.	Fuels performance cars and turbo models like the Ford Mustang GT and BMW 3 Series.
Typical Users	Chosen by everyday drivers seeking the lowest fuel cost for standard commuter cars.	Selected by owners of sports cars, luxury vehicles, and turbocharged models that require it.
Misfueling Risk	Putting regular in a premium-required engine can trigger knock and reduced power.	Putting premium in a regular engine wastes money but causes no mechanical damage.
Ethanol Content	Contains up to 10% ethanol in standard E10 blends across most US states.	Contains the same up to 10% ethanol content as regular in most standard blends.
Environmental Impact	Produces identical CO2 emissions per gallon burned as premium gasoline.	Emits the same CO2 per gallon as regular, offering no inherent environmental benefit.
Best-Fit Scenario	Best for economy cars and daily drivers whose manuals specify 87 octane fuel.	Best for turbocharged, high-compression, or high-performance engines that demand it.

What Is Regular Gas?

Regular gas is the standard, lowest-octane automotive fuel sold at filling stations, typically rated at 87 octane. It powers most everyday vehicles by igniting in the engine's cylinders to create combustion. It exists to provide an affordable, efficient fuel option for engines designed to run on lower compression.

Definition of Regular Gas

Regular gas is a refined petroleum distillate with an octane rating of 87, formulated for spark-ignition internal combustion engines. Its octane level measures the fuel's resistance to pre-ignition or knocking during compression. Engines with lower compression ratios operate safely and efficiently using this standard-grade fuel without requiring higher-octane alternatives.

Key Characteristics of Regular Gas

Characteristic	What It Means in Practice
87 Octane Rating	Resists knocking adequately for most standard passenger vehicles on the road today.
Lower Cost	Typically costs 20-40 cents less per gallon than premium at most stations.
Universal Availability	Sold at virtually every gas station nationwide, making refueling convenient anywhere.
Standard Compression Fit	Matches engines with compression ratios under roughly 10.5:1 without issues.
Contains Detergents	Meets EPA minimum detergent standards to help keep engine intake valves clean.
Higher Energy Density	Often contains slightly more energy per gallon than ethanol-blended premium alternatives.
Ethanol Blend Common	Usually contains up to 10% ethanol, which raises octane slightly while reducing energy.
Recommended by Manuals	Most owner's manuals specify regular for vehicles not requiring higher performance.
Shorter Shelf Life	Degrades faster than premium when stored, making it less ideal for long-term storage.
Lower Ignition Tolerance	Pre-ignites more easily under high heat or heavy load than higher-octane fuels.

Common Examples of Regular Gas

Shell V-Power NiTRO+ Regular - widely available 87-octane fuel with added friction-reducing technology.
Chevron with Techron Regular - uses Techron additive chemistry to clean fuel injectors and intake valves.
Exxon Regular - Synergy-branded 87-octane fuel sold at thousands of stations across the US.
Mobil Regular - shares Exxon's Synergy formulation with proven deposit-control additives.
BP Regular - Invigorate-branded fuel designed to help clean engines during normal driving.
Costco Kirkland Regular - Top Tier certified 87-octane fuel sold at discounted warehouse prices.
Sam's Club Regular - Top Tier certified fuel offering budget-friendly pricing for members.
Kroger Regular - grocery-chain fuel with fuel points rewards and consistent quality standards.
7-Eleven Regular - convenience-store fuel available at thousands of locations nationwide.
Circle K Regular - widely accessible 87-octane fuel with competitive everyday pricing.

Advantages and Limitations of Regular Gas

Advantages	Limitations
Significantly cheaper per fill-up, saving hundreds of dollars annually for average drivers.	Causes engine knocking or pinging in vehicles that explicitly require higher-octane fuel.
Works perfectly in the vast majority of cars, trucks, and SUVs on American roads.	Reduces performance and fuel economy in turbocharged or high-compression engines.
Available at essentially every fuel station, eliminating the need to hunt for specific brands.	Contains fewer detergents than some Top Tier premium fuels, allowing more carbon buildup.
Meets all EPA requirements for standard vehicle operation and emissions compliance.	Can cause long-term engine damage if used repeatedly in engines requiring premium.
Provides adequate knock resistance for engines with moderate compression ratios.	Offers slightly lower energy content than pure gasoline when blended with ethanol.
Compatible with flex-fuel vehicles when blended with up to 10% ethanol content.	Degrades more quickly in storage, losing combustibility within a few months.
Simplifies decision-making since most manufacturer recommendations default to regular.	Produces less power output in performance-oriented engines tuned for higher octane.
Reduces overall operating costs for fleet operators and high-mileage commuters.	May trigger check-engine lights in cars with knock sensors detecting pre-ignition events.
Supports consistent cold-start performance in standard naturally aspirated engines.	Performs poorly under extreme towing, hauling, or sustained high-speed driving conditions.
Offers environmental benefits through reduced refinery processing compared to premium.	Provides no cost benefit if the engine requires premium, since damage repairs cost more.

What Is Premium Gas?

Premium gas is a higher-octane fuel, typically rated at 91 to 93 octane, designed for high-performance and turbocharged engines. It resists pre-ignition and engine knock under high compression, ensuring smoother combustion. Premium gas exists to protect engines that require or benefit from increased octane under demanding driving conditions.

Definition of Premium Gas

Premium gas is a gasoline grade with an octane rating of 91 or higher, measured by the anti-knock index (AKI). Its higher octane allows the air-fuel mixture to withstand greater compression before igniting. This property prevents detonation in engines engineered for advanced ignition timing, forced induction, or higher cylinder pressures.

Key Characteristics of Premium Gas

Characteristic	What It Means in Practice
High octane rating	Resists premature combustion and engine knock under high stress and compression.
Higher cost	Typically costs 20 to 50 cents more per gallon than regular-grade fuel.
Detergent additives	Contains cleaning agents that help prevent carbon deposits on intake valves.
Slower burn rate	Burns more controllably, allowing advanced ignition timing in performance engines.
Turbocharger support	Prevents knock in forced-induction engines that generate intense cylinder heat.
High-compression tolerance	Handles the elevated pressures of modern direct-injection and performance engines.
No energy density boost	Does not contain more energy per gallon than regular fuel, so mileage stays similar.
Engine protection	Reduces the risk of detonation damage to pistons, rings, and bearings.
Consistent performance	Maintains peak horsepower and torque output in engines tuned for high octane.
Not universal necessity	Provides no measurable benefit in engines designed to run on 87 octane fuel.

Common Examples of Premium Gas

Shell V-Power NiTRO+ Premium – a 93-octane fuel with active cleaning technology for engine deposits.
Chevron Supreme Plus – a 93-octane premium with Techron additive for deposit control.
ExxonMobil Synergy Supreme+ – a premium grade with friction modifiers for engine wear protection.
BP Ultimate – a high-octane fuel formulated to clean and protect critical engine components.
Costco Kirkland Signature Premium – a Top Tier certified 93-octane fuel sold at lower prices.
Sunoco Ultra 93 – a high-octane option popular among enthusiasts and track-day drivers.
Marathon Supreme – a premium fuel with a detergent package meeting Top Tier standards.
Kroger Premium – a supermarket-brand 93-octane fuel offering value without sacrificing quality.
76 Premium – a high-octane gasoline with a cleaning additive package for engine longevity.
Mobil Supreme – a premium fuel engineered for high-compression and turbocharged engines.

Advantages and Limitations of Premium Gas

Advantages	Limitations
Prevents engine knock in high-compression and turbocharged engines under load.	Costs significantly more per gallon with no fuel economy benefit in most cars.
Allows engines to run at full rated horsepower and torque output.	Provides zero measurable performance gain in engines tuned for 87 octane.
Reduces the risk of long-term detonation damage to pistons and bearings.	Wasted money if your owner's manual only recommends, not requires, premium fuel.
Contains higher levels of detergent additives that keep intake valves cleaner.	Does not increase energy density, so it cannot improve miles per gallon.
Supports advanced ignition timing for smoother power delivery in performance cars.	Harder to find at rural stations or in regions where 93 octane is unavailable.
Helps maintain consistent performance during hot weather or heavy towing.	Accidental use in a regular-fuel car simply burns cleaner, offering no benefit.
Protects turbocharged engines from pre-ignition under sustained boost pressure.	Higher price per tank adds up to hundreds of extra dollars annually.
Often certified as Top Tier fuel with stricter quality and additive standards.	Modern engine computers can adapt to regular gas, negating any premium advantage.
Reduces carbon buildup on direct-injection engine intake valves over time.	No independent evidence shows it extends engine life in engines not requiring it.
Provides peace of mind for drivers of high-performance European and luxury vehicles.	Mixing premium with regular in a required-premium car still risks knock under load.

Similarities Between Regular Gas and Premium Gas

Shared Aspect	How Regular Gas and Premium Gas Are Alike
Fuel Purpose	Regular gas and premium gas both serve as combustible fuel to power internal combustion engines in vehicles.
Base Material	Regular gas and premium gas both derive from crude oil through the same petroleum refining process.
Chemical Family	Regular gas and premium gas both belong to the hydrocarbon family, primarily containing octane and other alkanes.
Energy Output	Regular gas and premium gas both release comparable thermal energy when burned, measured in BTUs per gallon.
Combustion Type	Regular gas and premium gas both undergo controlled combustion inside spark-ignition gasoline engines.
Delivery Method	Regular gas and premium gas both flow through the same fuel pump, lines, and injectors into the engine.
Storage Form	Regular gas and premium gas both remain liquid at standard atmospheric temperature and pressure conditions.
Vehicle Compatibility	Regular gas and premium gas both fit standard gasoline filler necks and work in most modern cars.
Refueling Process	Regular gas and premium gas both dispense from identical nozzles at the same gas station pumps.
Measurement Units	Regular gas and premium gas both sell by the gallon in the United States and by liter elsewhere.
Octane Scale	Regular gas and premium gas both use the same octane rating scale to measure their anti-knock properties.
Regulatory Oversight	Regular gas and premium gas both comply with government fuel standards set by agencies like the EPA.
Additive Package	Regular gas and premium gas both contain detergent additives designed to keep engine valves and fuel systems clean.
Seasonal Blending	Regular gas and premium gas both switch to winter and summer formulations to meet vapor pressure regulations.
Evaporation Risk	Regular gas and premium gas both evaporate over time, losing volatile compounds during extended storage.
Water Contamination	Regular gas and premium gas both absorb moisture from air, risking phase separation in fuel tanks.
Flammability Class	Regular gas and premium gas both carry the same highly flammable liquid classification for transport and handling.
Safety Handling	Regular gas and premium gas both require identical precautions against sparks, flames, and inhalation exposure.
Price Variability	Regular gas and premium gas both fluctuate in price daily based on global crude oil market conditions.
Tax Structure	Regular gas and premium gas both incur the same federal, state, and local excise taxes per gallon sold.
Combustion Byproducts	Regular gas and premium gas both produce carbon dioxide, water vapor, and trace emissions when burned.
Environmental Impact	Regular gas and premium gas both contribute to greenhouse gas emissions and local air pollution when combusted.
Mileage Potential	Regular gas and premium gas both deliver similar fuel economy in engines designed to run on either grade.
Cold Start Behavior	Regular gas and premium gas both ignite reliably in cold weather when the engine's fuel system operates correctly.
Engine Wear	Regular gas and premium gas both provide adequate lubrication protection for cylinder walls and piston rings.
Spark Plug Needs	Regular gas and premium gas both require functioning spark plugs to initiate the combustion process effectively.
Fuel Filter Fit	Regular gas and premium gas both pass through the same fuel filter, trapping debris before reaching the engine.
Storage Lifespan	Regular gas and premium gas both degrade within roughly three to six months when left unused in a tank.
Retail Availability	Regular gas and premium gas both appear at nearly every fueling station alongside mid-grade gasoline options.
Consumer Choice	Regular gas and premium gas both give drivers a legitimate fueling option based on their owner's manual guidance.

Regular Gas or Premium Gas: Which Should You Choose?

The single variable that decides it is your owner's manual. If the manual says "premium required," use premium gas. If it says "regular recommended," regular gas is the correct, cost-effective choice for nearly all drivers.

When to Use Regular Gas

Choose Regular Gas when your owner's manual states regular is recommended or required. Use it for standard commuting, highway driving, and everyday errands. Choose Regular Gas if your engine has no turbocharger and you want the lowest cost per mile.

When to Use Premium Gas

Choose Premium Gas when your owner's manual explicitly requires it, typically for turbocharged or high-compression engines. Use it to prevent engine knock, protect your warranty, and maintain peak performance. Choose Premium Gas if you hear knocking or pinging with regular fuel.

Common Misconceptions About Regular Gas and Premium Gas

Common Myth	The Reality
Premium gas always delivers more power in any car.	Premium gas only boosts power in engines designed for high compression; regular gas cars gain zero horsepower from it.
Using premium gas cleans your engine better than regular gas.	Both regular gas and premium gas meet the same detergent standards, so neither cleans your engine more effectively than the other.
Premium gas has a higher energy content than regular gas.	Premium gas and regular gas contain nearly identical energy per gallon; higher octane prevents knocking, not extra power.
Mixing regular gas and premium gas will damage your fuel system.	Mixing regular gas and premium gas is safe; the result simply has an octane rating between the two fuels.
You must use premium gas once you have used it before.	Switching between regular gas and premium gas freely is harmless; your engine adjusts to whatever octane you provide.
Premium gas is thicker or heavier than regular gas.	Regular gas and premium gas have similar density and viscosity; octane rating is a measure of knock resistance, not thickness.
Premium gas will fix a rough idle or engine hesitation.	Rough idling usually comes from spark plugs or sensors; regular gas or premium gas will not cure mechanical or ignition faults.
All sports cars absolutely require premium gas to run.	Some sports cars run fine on regular gas; only check your owner's manual to confirm the required octane for your engine.
Premium gas improves your fuel economy significantly over regular gas.	Premium gas may improve mileage by one or two percent in tuned engines, but regular gas gives identical economy in standard cars.
Higher octane means the fuel burns hotter than regular gas.	Premium gas burns cooler and more slowly than regular gas, which is exactly why it resists pre-ignition and knocking.
Using regular gas in a premium car will instantly destroy the engine.	Regular gas in a premium-required car causes knocking and reduced performance, but modern engines retard timing to prevent immediate damage.
Premium gas is worth it for every driver regardless of car type.	Premium gas wastes money in cars designed for regular gas; you gain no performance, economy, or longevity benefit.
Premium gas has more additives than regular gas.	Regular gas and premium gas use similar additive packages; the primary difference is octane, not the amount of detergents.
You can tell the difference between regular gas and premium gas by smell.	Regular gas and premium gas smell identical; octane rating is invisible and odorless, so you cannot detect it by senses.
Premium gas prevents all engine knocking in any vehicle.	Premium gas prevents knocking only in engines that require high octane; regular gas already prevents knocking in standard engines.
Older cars always need premium gas to run properly.	Most older cars run fine on regular gas; only high-compression classics or turbocharged models actually require premium gas.
Premium gas will make your car start faster in cold weather.	Cold starts depend on battery and spark; regular gas and premium gas ignite similarly at low temperatures, so start speed is unchanged.
Using premium gas once a month cleans your fuel injectors.	Regular gas with detergent additives cleans injectors continuously; occasional premium gas use provides no extra cleaning benefit.
Premium gas is the same product as regular gas with a different label.	Premium gas has a higher octane rating than regular gas, meaning it resists compression ignition better under high engine loads.
Your car will run quieter on premium gas than on regular gas.	Engine noise is identical on regular gas and premium gas unless knocking occurs, which only happens in engines needing higher octane.
Premium gas reduces harmful emissions compared to regular gas.	Regular gas and premium gas produce similar emissions; modern catalytic converters handle pollutants regardless of which octane you burn.
Small cars never benefit from premium gas under any condition.	Small turbocharged cars may require premium gas; engine design matters more than vehicle size when choosing between regular gas and premium gas.
Premium gas has a longer shelf life than regular gas.	Regular gas and premium gas degrade at similar rates; both lose volatility within months, so neither stores significantly longer.
You should always use premium gas when towing a trailer.	Towing increases engine load, but regular gas suffices unless your owner's manual specifies premium gas for your particular engine.
Premium gas is required for all turbocharged engines.	Some turbocharged engines run safely on regular gas; check the fuel door or manual, as boost pressure alone does not dictate octane need.
Premium gas prevents carbon buildup in direct injection engines.	Carbon buildup on intake valves occurs with regular gas and premium gas alike; neither fuel type prevents this maintenance issue.
Using regular gas voids your car warranty.	Using regular gas does not void a warranty unless your owner's manual explicitly requires premium gas for your specific engine.
Premium gas makes your engine run at a cooler temperature.	Premium gas resists knocking but does not lower overall engine temperature; cooling systems manage heat regardless of octane choice.
You can boost regular gas octane by adding premium gas to the tank.	Adding premium gas to regular gas raises the blend's octane proportionally, but it never reaches full premium gas rating unless the tank is mostly full.
Premium gas is a myth and never benefits any engine.	Premium gas delivers real benefits in high-compression or turbocharged engines, where regular gas would cause knocking and lost performance.

Conclusion

Difference Between Regular Gas and Premium Gas comes down to octane rating, not quality. Choose regular for standard engines to save money. Choose premium only when your owner's manual requires it, preventing knock and protecting performance.

FAQs on Difference Between Regular Gas and Premium Gas

What is the difference between regular gas and premium gas?: The difference is the octane rating, with regular gas at 87 and premium gas typically at 91 to 93, which measures the fuel's resistance to engine knocking.
Which is better, regular gas or premium gas?: Neither is universally better; premium gas is better only for engines that require it, while regular gas is better for engines designed to run on lower octane.
Is premium gas worth the extra cost?: No, premium gas is not worth the extra cost for vehicles that only require regular gas, because it provides no measurable performance or fuel economy benefit in those engines.
Can I use regular gas instead of premium gas?: Yes, you can use regular gas instead of premium gas only in an emergency, but doing so consistently in a required engine risks knocking, reduced power, and potential long-term damage.
What happens if I accidentally put regular gas in a premium car?: If you accidentally put regular gas in a premium car, the engine's knock sensors will adjust timing to prevent damage, but you may notice reduced power and lower fuel economy.
Does premium gas give better gas mileage than regular gas?: No, premium gas does not give better gas mileage than regular gas in an engine designed for regular, because octane rating does not affect fuel energy content.
How do I know if my car needs premium gas?: You know your car needs premium gas if the owner's manual or the fuel filler door explicitly states "premium fuel required," not merely "recommended."
Is it safe to mix regular gas and premium gas in the same tank?: Yes, it is safe to mix regular gas and premium gas in the same tank, because the blend simply results in an intermediate octane rating that is generally harmless.
Can I switch back and forth between regular and premium gas?: Yes, you can switch back and forth between regular and premium gas, because modern engines adapt to the octane level, provided you use premium when the manual requires it.
Why do some cars require premium gas while others use regular gas?: Some cars require premium gas because they have high-compression or turbocharged engines that need higher octane to prevent pre-ignition and knocking under load.