Dive Brief:

• Costco Wholesale consistently beats Amazon on price, sometimes by huge margins, according to research from online student loan refinancing marketplace LendEDU. Items on Amazon on average are 56.48% more expensive than the same products found at a Costco store shopped by LendEDU researchers.

• When LendEDU Research Analyst Mike Brown gathered all 38 of the items he analyzed in one basket, he found that the total price on Amazon was 12.1% higher than buying the same basket of things at Costco. Mixing up categories showed similar results. In a "miscellaneous" basket (including consumer products, pet food, men’s socks and pens), shopping on Amazon proved to be on the whole 81.38% more expensive than Costco.

• “The study issued by LendEDU is flawed and misleading, and based on incomplete data," an Amazon spokesperson told Retail Dive, after being sent LendEDU's study. "Amazon’s prices are as low or lower than any other retailer and we work hard for customers to ensure that’s true every day. In addition to low prices, we offer customers a vast selection, and more than 100 million items that are eligible for free shipping to all customers, every day.

Dive Insight:

With Walmart aggressively fueling its e-commerce sales and moving to assertively defend its status as a low-price leader, much is being made of how drastically it’s narrowed its price differential with Amazon. Research from retail data analytics firm Market Track and e-commerce analytics firm Profitero in recent weeks have found Walmart getting much closer to Amazon’s prices and even beating in some categories.

But LendEDU’s research shows Costco consistently outgunning Amazon on price. Both by average price difference and total price difference, the widest price discrepancy favoring Costco was in food and beverage purchases. On average, food and beverage products from Amazon were 120.15% more expensive when compared to the same goods at Costco. The difference was much narrower when it comes to technology products, though Costco still proved cheaper (2.23% across the category) on the whole.

"The ability to save the consumer money has driven the astronomical success for both Costco and Amazon, but which saves you more money? Judging from these results, consumers would be best served purchasing their food and beverage items from Costco Wholesale instead of on Amazon," Brown said in a blog post on his research. However, he added that with Amazon beating Costco on some electronics, consumers "might be better served browsing Amazon first when shopping for the many gadgets of 2017."

Costco is widely seen as benefiting from a treasure hunt atmosphere, where shoppers pick things off the shelves not originally on their shopping list. That, as well as its membership fees, are its saving grace — on some items Costco makes no money. It’s essentially how Amazon operates, too, with its Prime members more or less paying for shipping costs up front.

Amazon’s dynamic pricing may be an advantage for the e-commerce giant in the online world. The Amazon spokesperson didn't describe how that worked, but addressed it to Retail Dive this way: “Retail prices fluctuate all the time, and Amazon seeks to meet or beat the lowest competitive price for our customers.”

In any case, to the extent that dynamic pricing enables any e-commerce retailer to swiftly, if not automatically, adjust prices, Costco, (which has quietly been building its e-commerce sales but remains focused on brick and mortar), can’t really do the same in stores.

It all adds up to a potential price war among retailers, as long as shoppers are willing to frequent different retailers — and, according to research from Frank N. Magid Associates, Costco and Amazon shoppers typically do shop around. (Meanwhile, Walmart's shoppers, who are more fixated on price and convenience, stick to Walmart.)

"This year there's been a marked rise in discussion about an online price war," Keith Anderson, Profitero senior vice president of strategy and insights, said of his firms study in October. "While lower prices are good news for shoppers, suppliers and retailers will inevitably feel the pressure as we head into peak holiday season, as this price war is only set to intensify."

This post has been updated to reflect Amazon's comments on the study and its description of "dynamic pricing."