Gas mileage wasn't always a concern for automobile drivers as the first automobiles were much less efficient than they are now. Following the Clean Air Act, the formation of the Environmental Protection Agency and oil crises of the 1970s and 1980s, it became a concern as people became more aware of fuel conservation and the environmental impact of vehicle emissions.
Miles Per Gallon or GPM?
The standard way to measure fuel economy is through MPG, which is how many miles a car can go on one gallon of gas. MPG ratings are typically higher on the freeway versus the city. City driving requires a lot of slow speeds with higher RPM, plus a lot of idling, which drains gas without much movement. Therefore, most vehicles get at least five MPG more on the highway versus the city.
The GPM rating is something conceived by Edmunds to figure out how many gallons the vehicle needs to drive 100 miles. For example, if a vehicle is rated at 12.5 GPM, it needs eight gallons of fuel to go 100 miles. Some consider this a better method of determining a fuel-efficient vehicle than miles per gallon.
Does Octane Affect MPG?
With the introduction of catalytic converters in U.S. vehicles in the 1970s, vehicles started to run almost exclusively on unleaded gas instead of leaded. That allowed engines to have a cleaner operation, which had the additional effect of increasing gas mileage. The octane rating of unleaded gasoline can also affect it. When you go to the gas station, you might see that there are numbers on each pump. The lowest is usually 87 octane. The higher the octane rating, the slower the gas burns, which makes the vehicle run more efficiently. However, most vehicles only require 87 octane gas, and the higher octane gas has a negligible effect on MPG in most cases. On the other hand, vehicles that require or recommend higher octane gas may see a significant loss of MPG by using 87 octane instead of the higher numbers. Higher octane gas costs more, but it may translate into savings with better gas mileage.
Cars Versus Trucks
It's no secret that passenger cars tend to get better fuel economy than trucks and SUVs. What is the reason for this? The main reason is that cars are built on a unibody chassis and trucks are typically made with a body mounted on the frame. That's part of the reason why modern, car-based SUVs tend to get much better gas mileage than earlier, truck-based models. Small SUVs like the Toyota RAV4 and Honda CR-V were among the first to be built on a passenger car chassis and saw increased fuel efficiency. With the emergence of crossover SUVs in the present day, more and more SUVs are being built on car chassis and are typically much more fuel-efficient than the few remaining body-on-frame SUVs.
Hybrid Fuel Efficiency
The other type of extremely fuel-efficient vehicle is a hybrid. These vehicles use both a gas engine and an electric engine. The electric motor typically runs the car at idle or slow speeds before the gasoline engine takes over or supplements the motor. As previously mentioned, most vehicles lose significant fuel economy driving at slow speeds in the city. Hybrids can run cleaner and more efficiently in situations where full gas vehicles cannot. Hybrids have become more prevalent in the present day, and there are also plenty of hybrid SUVs and larger cars available now.
Driver Ability Effect On Gas Mileage
The other factor in good gas mileage is how you drive. Aggressive drivers who drive at higher rates of speed typically see much worse fuel economy to those who drive at a lower rate of speed and without a lot of hard acceleration. For example, accelerating quickly from a full stop burns a lot more gas than getting up to speed slowly and steadily. Similarly, if you constantly tailgate and have to step on the brakes and then speed up again, you're also burning more gas. Driving more steadily tends to yield quite a bit of gas savings.
Vehicle Condition And Fuel Economy
Another effect on fuel economy is the condition of the vehicle in question. A well-maintained and newer vehicle is likely to get better gas mileage than one that is in poor condition or has a lot of miles. Changing the oil and oil filter regularly and keeping tires at proper inflation is essential for getting good gas mileage. It's also a good idea to run injector cleaners from time to time to keep those from becoming clogged and reducing fuel economy.
Fuel Economy By Type
It's easy enough to say that a vehicle getting 50 MPG on the highway is a very fuel-efficient vehicle. However, not everyone can drive the same type of vehicle. Therefore, it's useful to look at what fuel economy rating is suitable for certain types of vehicles. Not only that, but different people in different situations may have a particular idea of what good fuel economy is to them. Getting 15 MPG driving around town might be entirely acceptable for some people as good fuel economy. For others, this might be low. For example, a 2019 Porsche Boxster gets 25 MPG combined city and highway, while a 2019 Honda Accord LX gets 31 MPG combined. At first glance, you'd likely say that the Accord gets better MPG, which is technically correct. But 24 MPG combined for a sports car is not bad. And most people do not buy sports cars or full-size trucks on their excellent fuel economy.
Most Fuel-Efficient Passenger Cars Including Electric Cars
According to the EPA, the following vehicles are the most fuel-efficient passenger cars in each class:
Two-Seaters - Smart EQ Fortwo (coupe) 108 MPG combined
Minicompacts - Fiat 500e 112 MPG combined
Subcompacts - BMW i3 113 MPG combined
Compacts - Volkswagen e-Golf 119 MPG combined
Midsize - Hyundai Ioniq Electric 136 MPG combined
Large - Tesla Model S Long Range 111 MPG combined
Small Station Wagons - Chevrolet Bolt EV 119 MPG combined
Midsize Station Wagons - Volvo V90 FWD 27 MPG combined
The only category without an electric vehicle is that of the midsize station wagon, which is why the MPG goes down drastically.
Most Fuel-Efficient Passenger Cars Excluding Electric Cars
To compare, let's look at the fuel efficiency of small passenger cars that are not electric.
According to the EPA, these are the most fuel-efficient cars by class:
Two-Seaters - Fiat 124 Spider and Mazda MX-5 30 MPG combined
Minicompacts - MINI Cooper Convertible 31 MPG combined
Subcompacts - Chevrolet Spark 33 MPG combined
Compacts - Toyota Prius C Hybrid 46 MPG combined
Midsize - Toyota Prius Eco Hybrid 56 MPG combined
Large - Hyundai Ioniq Blue Hybrid 58 MPG combined
Small Station Wagons - Kia Niro FE Hybrid 50 MPG combined
Midsize Station Wagons - Volvo V90 FWD 27 MPG combined
You might think compact cars would get better MPG, but due to the presence of hybrids in this list, the more substantial cars fare better.
Fuel-Efficient Muscle Cars
Muscle cars typically are more massive and put out more horsepower than something falling in the roadster sports car category. For example, the Mazda MX-5 Miata gets a 30 MPG city/highway combined rating from the EPA but weighs less than some compact hatchbacks. On the other hand, the Mercedes-AMG C63 S offers a 503 horsepower turbocharged V8 engine, and it gets 20 MPG combined. A BMW M4 has 425 horsepower from a turbocharged six-cylinder engine and gets roughly the same combined MPG. The Nissan 370Z gets 22 MPG combined with its 3.7-liter V6 engine and six-speed manual transmission.
Some high-performance cars can use more advanced technology to extract more efficiency out of big engines. Some versions of the Chevrolet Corvette Stingray, for example, achieve up to 29 MPG highway through cylinder deactivation, allowing it to run on only four cylinders in highway cruising situations. However, this technology is typically found on more expensive vehicles.
Most Fuel-Efficient Trucks, Vans and SUVs
The other vehicle categories that typically offer lower MPG are trucks, SUVs and minivans or regular vans. Similar to muscle cars, you can't reasonably expect to get much more than 20 MPG overall in a non-hybrid, and few offer more than 30 MPG even on the highway.
The list of vehicles that are not electric from the EPA seems to bear that out as follows:
Small Pickup Trucks - Chevrolet Colorado 2WD Diesel and GMC Canyon 2WD Diesel 23 MPG combined
Standard Pickup Trucks - Ford F150 Pickup 2WD Diesel 25 MPG combined
Small Sport Utility Vehicles - Toyota RAV4 Hybrid AWD 40 MPG combined
Standard SUVs - Lexus RX 450h AWD Hybrid 30 MPG combined
Minivans - Chrysler Pacifica, Honda Odyssey and Toyota Sienna 2WD 22 MPG combined
The primary factor bringing the overall MPG of these vehicles down is their city driving efficiency. For example, the Colorado LT Diesel gets a relatively impressive 30 MPG on the highway, but it only manages 20 MPG in city driving. The F-150 also gets only 30 MPG on the highway but achieves a slightly higher 22 MPG city mileage. Further, all of the standouts in the SUV category are hybrids. When you look at a standard SUV like the Jeep Grand Cherokee Trackhawk with a V8, it only gets 13 MPG combined.
In summary, the question of what is good gas mileage depends on a lot of factors, including driving situation, vehicle type and condition, and the driver's ability.