Costco broke gas station sales records in Q3 as drivers chased lower pump prices and many of them were buying gas at the warehouse club for the first time. Chief Executive Ron Vachris said the spike came as the Middle East war pushed fuel prices higher, pulling more cars into Costco’s lots and helping lift the company’s reported revenue by 12%.

The rush makes sense because the savings can be real. Regular gas hit about $4.48 a gallon in late May, roughly $1.32 higher than a year earlier, after three years of declines gave way to a reversal. Costco pumps typically undercut nearby stations by 10 to 30 cents a gallon, and Patrick De Haan said Costco tends to be one of the most aggressive competitors when it comes to prices.

That advantage comes from how the warehouse club sells fuel. Doug Johnson said Costco keeps prices down by accepting a thinner margin than rivals, putting its fuel margin at 14% compared with an industry standard of 20%. The company’s pitch works best when drivers can get in, fill up and leave without burning time or miles getting there.

That is where the math gets messier. De Haan said long wait times and longer drives can wipe out the savings, and the $65 membership fee can make the calculation even harder for drivers who do not use Costco often. Kiplinger estimates a Costco Gold member would need to buy between 260 and 1,300 gallons a year to break even on the fee, a wide range that depends on how much a driver actually fills up and how much those trips are worth.

Vachris said the gas traffic does not stop at the pumps. Customers who buy fuel at Costco tend to spend more inside the store, and that added foot traffic gives the company another way to turn cheap gas into sales. Independent price checks have also found that Costco’s warehouse items were 8% cheaper than Walmart and 13% cheaper than Target, while BJ’s items were priced 15% cheaper than Walmart’s, with shoppers often saying Costco’s goods felt higher-quality.

The open question is how much of this record demand lasts if fuel prices ease. For now, the higher price at the pump is doing double duty for Costco: drawing first-time gas buyers into the lot and sending some of them back inside with a cart.