Why Your Car’s Fuel Efficiency Isn’t What You Think It Is

Imagine you’re shopping for a car. You see two options:

• Car A: Upgrades from 34 MPG to 50 MPG
• Car B: Upgrades from 12 MPG to 14 MPG

Which one saves more gas?

Most people pick Car A. After all, 50 MPG sounds amazing compared to 14 MPG. But here’s the plot twist: Car B actually saves more fuel.

Sounds crazy, right? This is the MPG illusion at work—a cognitive trap that even the smartest among us fall into. It’s a mental shortcut that tricks us into believing MPG (miles per gallon) tells us how much gas we’ll save, when in reality, it doesn’t.

Researchers Richard P. Larrick and Jack B. Soll from Duke University exposed this illusion in their groundbreaking study, showing just how flawed our thinking about fuel efficiency really is. And the implications go far beyond car shopping—they affect our wallets, the environment, and even government policy.

The Hidden Cost of a Simple Math Error

For decades, we’ve been conditioned to think in MPG. But MPG is misleading because fuel savings aren’t linear—they’re curved.

Think of it this way: Going from 10 to 20 MPG cuts your fuel use in half, but going from 50 to 100 MPG barely makes a dent. The real measure of fuel efficiency isn’t how far you can drive on a gallon—it’s how many gallons you need to drive a set distance.

In other words, instead of MPG, we should be thinking in terms of gallons per mile (GPM)—or better yet, gallons per 100 miles (the metric system’s standard uses litres per 100 km).

But since most of us don’t, we end up wasting money and gas by making poor choices.

The Experiment

To prove just how deeply the MPG illusion affects decision-making, Larrick and Soll conducted a series of experiments.

?? Experiment 1: Asked 77 college students to rank which car upgrades saved the most fuel. 60% of them got it wrong.

?? Experiment 2: Had 74 participants decide how much they would pay for cars with different MPG ratings. Most people overpaid for high MPG cars, thinking they saved more gas than they actually did.

?? Experiment 3: A larger sample of 171 participants had to choose between two policies for replacing town fleet vehicles. When fuel efficiency was presented in GPM instead of MPG, the percentage of people making the correct decision jumped from 25% to 64%.

The conclusion? MPG distorts our ability to judge fuel savings. And unless we shift to a better system, we’ll keep making bad decisions.

How This Affects You (And How to Fix It)

So, what does this mean for your next car purchase? It means you should forget about MPG and start thinking in terms of actual fuel consumption. Here’s how:

? Look at Gallons per 100 Miles (GPM) – Countries like Canada and most of Europe already use liters per 100 km, which is much clearer.

? Prioritize Upgrading Low-MPG Cars – If you’re upgrading, focus on improving the worst performers first. Going from 15 to 20 MPG saves way more gas than going from 40 to 50 MPG.

? Calculate Yearly Fuel Use, Not Just MPG – Before choosing a car, figure out how many gallons (or liters) you’ll actually use per year. The real savings will surprise you.

? Push for Better Fuel Economy Labels – Governments and automakers should switch to GPM to help consumers make better choices.

The MPG Illusion Is Everywhere

The MPG illusion isn’t just about cars. It’s about how we perceive numbers and efficiency in every aspect of life. Advertisers use similar tricks to shape our decisions—whether it’s how much money we’ll save on a “discount” or how much healthier a product is compared to another.

Consider ads that promise “50% more product” or “twice the speed.” These numbers sound impressive, but without context, they can be misleading. Just like with MPG, the key question should always be: What does this number actually mean in practical terms?

Next time you see a flashy high-MPG number or a bold advertising claim, pause for a moment. Ask yourself: How much real value am I getting? Because in a world where marketing thrives on perception, understanding the truth behind the numbers could save you thousands—not just on fuel, but on everything you buy. ??????

?? Further Reading: The MPG Illusion Study