For some of your food shopping, membership warehouse clubs offer low-cost alternatives to supermarkets. Using our market basket of 150+ grocery items, we surveyed prices in seven metro areas for BJ’s, Costco, and Sam’s Club and compared them to Walmart, Target, and traditional supermarkets.

The warehouse stores carried few if any of the items in our market basket in the usual sizes, but when we looked for the same brands regardless of size, warehouse stores, which specialize in bulk sales, stocked a larger portion of our market basket items.

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Since the warehouse stores stocked so few items in the sizes of our basic market basket, we looked for items of any size, so long as they were the same brands. We then used unit prices (for example, price per pound) to calculate the warehouse stores’ prices for amounts specified in the market basket. After this adjustment, we compared the prices of items at the warehouse stores with prices for the same brands at several other stores. Bear in mind that this is not an “apples-to-apples” comparison; the sizes of the items priced at the warehouse stores were almost always larger than the sizes of the items priced at the other stores, so the warehouse stores enjoy an advantage in such a comparison.

We found the warehouse clubs all offer significant savings. Costco and Sam's Club beat most of the supermarket chains' prices by 20 to 35 percent. BJ's offered less savings than its two national warehouse competitors, but still saved us a lot off most grocers' prices.

In addition to having low prices, Costco received much higher ratings than many of its competitors when we asked consumers to rate it for the quality of its fresh meats.

While the warehouse clubs typically offered significant savings compared to prices offered at grocery stores, these savings perhaps aren’t enough to justify paying the clubs’ annual membership fees if you don’t use them often. And if half of what you buy is wasted due to spoilage, you won’t save by buying in bulk.