It used to be that a warehouse club membership was a necessity for suburban families: depending on where they lived, they might belong to BJ’s, Costco, or Sam’s Club, or some combination of the three. Yet while warehouse club membership has stayed pretty steady over the last few years, membership in Amazon Prime has increased instead.

That leads retail-watchers to wonder: is Prime the new warehouse club membership?

While Prime doesn’t necessarily entitle shoppers to load up their cars with dozens of rolls of toilet paper and barrels of honey, it’s the same model as warehouse clubs, giving members access to merchandise or discounts not available to the public, as well as other benefits.

According to a research note from investment firm Cowen and Company (via Business Insider), the percentage of households in the U.S. that have Amazon Prime has risen significantly in just the last four years, while the percentage who have memberships in warehouse clubs hasn’t changed by very much.

That means there’s a big overlap between the two categories, but that there must also be a few people dropping their warehouse club memberships in favor of Prime, depending on what benefits they receive back and how useful the services are to them. The number of Prime members has doubled over that time, but Cowen estimates that there are around 50 million Prime members, about twice what there were last year.

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