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It’s an argument that’s as old as the hills: Assuming you can only pick one, should you shop at Costco or Sam’s Club?

On the one hand, Costco offers more services than Sam’s Club, including car and home insurance. On the other hand, Sam’s Club’s basic membership is cheaper than Costco ($50 vs. $65) and it offers curbside pickup and a more robust mobile app. While Costco’s Executive membership is also pricier ($130 vs. $110 for a Sam’s Club Plus membership), its 2% cash back benefit is capped at $1,250 per year, while Sam’s Club limits rewards to $500 annually.

Although the warehouse clubs are neck and neck for most products and services, Costco typically comes out ahead at the pump. This is because the quality of Costco’s gas is better for your engine. If this is news to you, let’s take a look at why Costco’s gas might be better than Sam’s Club.

Costco’s gas is a tier above Sam’s Club

Kirkland Signature gas (the gasoline available at Costco) is a part of what’s called TOP TIER™ fuel. Although many gas stations also sell TOP TIER™ fuel, notably Sam’s Club does not.

What’s all the fuss over TOP TIER™ fuel? For one, several tests have demonstrated its ability to help your engine run cleaner. In fact, its effectiveness has been proven so thoroughly that the AAA has even urged drivers to seek out TOP TIER™ gas stations, even when fuel is more expensive there.

According to AAA’s research, non-TOP-TIER™ gasoline creates 19 times more engine deposits than TOP TIER™ brands after only 4,000 miles of driving. These deposits can harm your engine’s performance, including reducing your fuel economy and increasing emissions. This is especially the case on newer vehicles, which are more vulnerable to the damaging effects of deposits.

In short, buying non-TOP-TIER™ gasoline frequently, even when the prices are cheaper, could become more expensive over long periods of time, as your reduced fuel economy could require you to stop and fill up more frequently.

Notably, the AAA doesn’t specify which make or model vehicle was used for this test, which could affect the final result. But when price remains the same — when gas at Costco is on par with Sam’s Club — the addition of TOP TIER™ gasoline at Costco represents a free benefit that could help your engine over the long run.

Price might also influence your decision to buy gas at Costco

To be honest, I’ve never seen a significant price difference between Costco and Sam’s Club gas. For example, in my area, regular gas at Costco costs $2.65 and premium is $3.39. Meanwhile, Sam’s Club has the exact same prices.

For those who have a Costco credit card, however, rewards and cash back earned could reduce your fuel costs significantly. Since Costco only accepts Visa cards, however, you’ll need to be strategic about which card you bring to the warehouse and its gas stations. Click here to learn how you can earn 3% cash back on Costco purchases and get a welcome bonus of up to $300 while you’re at it.

If you’re concerned about your engine’s health, it might be worth looking into TOP TIER™ gasoline. Certainly gas prices are a huge factor in deciding where to fuel up, but the long-term benefits of good quality gas could save you money on hidden costs and a potentially longer life on your vehicle.

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