Though Amazon has promised steep discounts at Whole Foods stores, now that it owns the organic supermarket chain, Costco still reigns supreme in the ongoing grocery price wars, according to JPMorgan.

“[Costco] offers an unquestioned value prop with the best pricing, curated assortment, strong private label offering, and treasure hunt atmosphere,” JPMorgan analyst Christopher Horvers wrote in a note to clients.

After completing price checks at each Costco, Whole Foods, Wal-Mart, Target and Aldi, Horvers and his team found Costco’s stickers, on a per-unit basis, to be a “whopping” 58 percent cheaper than those at Whole Foods.

Costco and Whole Foods share the least of their merchandise assortments in common, JPMorgan discovered, while Costco and Wal-Mart see the most overlap in their grocery stock keeping units, or SKUs.

To be sure, being a low-price leader comes with pros and cons. Investing in discounting can squeeze a retailer’s profit, and that’s what some investors worry about, as it relates to Costco.

Costco shares took a hit one week ago when the company posted narrowing gross margins and a fourth-quarter decline in membership renewal rates. Shoppers were seen buying more fuel, which is less profitable, at Costco during the latest period.

In June, when e-commerce giant Amazon first announced its plans to acquire Whole Foods, companies like Kroger, Sprouts Farmers Market, Supervalu, Albertsons and even Costco watched their stocks tumble.

Goldman Sachs was one of the first investment banks to react, immediately downgrading Costco shares on the news and adding to any arguments against Amazon’s retail rivals. One trading day later, Deutsche Bank followed suit with its own Costco downgrade.

The same group of grocery stocks dropped again, a few weeks later, when Amazon revealed it would be slashing prices across Whole Foods stores once the deal between the two was complete. Investors’ fears for Costco were seen ballooning.

Nonetheless, JPMorgan’s latest price checks point out that Whole Foods’ value proposition greatly contrasts that of Costco, still.

“It is clear that [Whole Foods’] pricing would need to narrow substantially to be a threat to COST, while the Whole Foods business model would need to shift away from its ‘foodie, organic, and natural’ value prop,” Horvers wrote.

When looking at baskets of perishable groceries, dry goods and household items — each from Costco, Whole Foods, Wal-Mart, Target and Aldi — Costco was consistently the least-expensive option, JPMorgan found.

Wal-Mart’s private-label products turned out to be the cheapest of the group when compared to national brands. But Costco’s Kirkland Signature nameplate is a stronger player than its peers when it comes to quality, Horvers added.

Costco faces an uphill battle from here in trying to win back lost confidence on the Street.

On a conference call with analysts and investors last week, Chief Financial Officer Richard Galanti said: “As it relates to the publicity and the news and the noise around Amazon and Whole Foods, all we can do is perform.”

One factor that would help is if value-minded consumers understood the price comparisons that JPMorgan uncovered.

Costco, with its massive stores, is trying to keep up with the shift online. The warehouse retailer recently launched two new delivery options for its members, one called Costco Grocery. The service offers shoppers about 500 non-perishable goods for two-day delivery, with orders over $75 dropped off at no charge.

A second service, offered in metropolitan markets and powered by Instacart, lets shoppers choose from 1,700 items, including fresh groceries, for same-day delivery.

Costco is the the third-largest grocery retailer in the U.S., after Wal-Mart, which is No. 1, and Kroger.

Costco shares are down about 1.8 percent this year.