It is common knowledge among savvy shoppers that you normally save for buying in bulk and for buying store brand. Under this principle, many shoppers will just grab the largest size store brand their pantry or fridge can store and move on.

Larger quantities see their price per ounce decrease as the company needs less plastic, glass, or paper per ounce sold to package it. However, while larger is normally cheaper, this principle is not universally true.

Furthermore, many shoppers have theories about which grocery store is the cheapest in town. Under this principle, they do all their shopping at one store. However, while some stores are normally cheaper, this principle is also not universally true.

In reality, grocery stores do not simply discount bulk, and different grocery stores will show savings to different shoppers based on their specific preferences.

Let’s take store brand extra virgin olive oil in Charlottesville, VA for example.

Here are the prices for the 5th Street Wegman’s store brand olive oil:

Ounces of Wegmans Italian Classics 100% Italian Extra Virgin Olive Oil	Price	Price / Ounce	Price for 101 fl oz
101 fl oz	$28.29	$0.28010	$28.29
33.8 fl oz	$11.29	$0.33402	$33.74
16.9 fl oz	$7.89	$0.46686	$47.15
Prices gathered on March 3 and confirmed on May 15, 2018 from Instacart.

 

You can see buying 101 fl oz is a whole $18.86 cheaper than buying the equivalent amount of 16.9 size. Presumably the 5 extra bottles the company had to make and package in the 16.9 size is the difference in price. The Wegman’s prices have a large difference in per unit cost between sizes.

Looking at Harris Teeter, you can see much lower prices, but also a strange discount for the 16.9 fl oz size. Here are the Barracks Road Harris Teeter’s store brand prices:

Ounces of Harris Teeter Extra Virgin Olive Oil	Price	Price / Ounce	Price for 101 fl oz
25.5 fl oz	$5.49	$0.21529	$21.74
16.9 fl oz	$3.49	$0.20651	$20.86
8.5 fl oz	$2.49	$0.29294	$29.59
Prices gathered on March 3 and confirmed on May 15, 2018 from Harris Teeter Online.

 

For some reason, the largest size at Harris Teeter (25.5 fl oz) costs $0.88 more than the equivalent amount of 16.9 fl oz size. My only charitable explanation is that the 16.9 fl oz is a very convenient size and likely popular among consumers. Thus, it might save the store money in ordering and restocking if they promote it.

At Kroger, the pricing gets weirder. Here are the prices for the Barracks Road Kroger:

Ounces of Kroger Extra Virgin Olive Oil	Price	Price / Ounce	Price for 101 fl oz
101 fl oz	$18.99	$0.18802	$18.99
51 fl oz	$8.49	$0.16647	$16.81
34 fl oz	$6.49	$0.19088	$19.28
25.5 fl oz	$5.49	$0.21529	$21.74
17 fl oz	$3.69	$0.21706	$21.92
8.5 fl oz	$2.69	$0.31647	$31.96
Prices gathered on March 3 and confirmed on May 15, 2018 from Kroger Online.

The 101 fl oz size is $2.18 more expensive than the equivalent amount of 51 fl oz size. I’m not sure why they are punishing people for buying the largest bulk size possible.

Here is Walmart’s pricing:

Great Value 100% Extra Virgin Olive Oil	Price	Price / Ounce	Price for 101 fl oz
101 oz	$15.14	$0.14990	$15.14
51 oz	$9.84	$0.19294	$19.49
25.5 oz	$5.94	$0.23571	$23.81
Prices gathered on May 15, 2018.

Then there is Costco. They have no store brand, only one name brand, and only one size.

Kirkland Signature Extra Virgin Olive Oil	Price	Price / Ounce	Price for 101 fl oz
70 fl oz	$16.99	$0.24271	$24.51
Prices gathered on May 15, 2018.

And Sam’s Club with their Member’s Mark brand:

Member’s Mark Extra Virgin Olive Oil	Price	Price / Ounce	Price for 101 fl oz
105 oz	$19.98	$0.19029	$19.22
70 oz	$15.28	$0.21829	$22.05
35 oz	$11.98	$0.34229	$34.57
Prices gathered on May 15, 2018.

 

When comparing grocery stores, Walmart and Kroger have the cheapest options. They beat both Costco and Sam’s Club, who are supposedly known for their bulk savings. Meanwhile, for those of us worried about storage and/or perishing, Harris Teeter has the cheapest non-bulk option.

Here are the cheapest size’s price at each grocery store:

	Price	Price / Ounce	Price for 101 fl oz
Wegmans (101 fl oz)	$28.29	$0.28010	$28.29
Costco (70 fl oz)	$16.99	$0.24271	$24.51
Harris Teeter (16.9 oz)	$3.49	$0.20651	$20.86
Sam’s Club (105 oz)	$19.98	$0.19029	$19.22
Kroger (51 fl oz)	$8.49	$0.16647	$16.81
Walmart (101 oz)	$15.14	$0.14990	$15.14

And here are each size’s cheapest brand and price:

Size	Brand	Price	Price / Ounce	Price for 101 fl oz
101oz	Walmart	$15.14	$0.14990	$15.14
70oz	Sam’s Club	$15.28	$0.21829	$22.05
51oz	Kroger	$8.49	$0.16647	$16.81
34oz	Kroger	$6.49	$0.19088	$19.28
25.5oz	Kroger or Harris Teeter	$5.49	$0.21529	$21.74
17oz	Harris Teeter	$3.49	$0.20651	$20.86
8.5oz	Harris Teeter	$2.49	$0.29294	$29.59

 

Now, the fact that I am comparing name brand olive oils shows I am not an olive oil connoisseur. As NPR has reported many times, “Your Olive Oil May Not Be The Virgin It Claims .” Many brands are apparently polluted by non-olive oils. An olive oil connoisseur might benefit from redoing this analysis, but looking just at one name brand olive oil like California Olive Ranch.

After hearing these stories, I tend to believe (perhaps naively ) that store brand olive oil are an okay bet as grocery stores have incentive to avoid scandal with their products. (For what it is worth, in 2002 Walmart’s Great Value Olive Oil won “Best Store Brand” olive oil from Cooking Light.)

Regardless, I think olive oil is a fascinating example that buying bulk doesn’t always save you money. Grocery stores know all the shoppers tricks, which means that when comparative price shopping you actually have to compare the prices of all the different sizes to purchase the best deal.

Hardcore shoppers will do studies like this for their big ticket items or frequent purchases and then create separate grocery lists for each store based on where the item they want is cheapest. For a tight budget family, olive oil might be one of those purchases as you can save $10 simply by stopping by a different store to pick it up.