Tracking Costco gas doesn't make much sense as Costco doesn't make money on gas. They use it as a loss-leader for memberships.

Watching prices makes sense.

People spend money on gas, and sometimes one Costco has cheaper gas than another does.

The two Costcos that are nearest to me are listed at $3.65 and $3.79 right now. They're ~25 minutes apart. I think it would be fair to say that there's thousands of people living in-between where the difference in driving distance is irrelevant.

But if they decide that buying gas is a thing they're going to do today, and they can quickly compare the prices beforehand, then: They can use that data to help make an informed decision.

A 14-cent price delta isn't much, but if 11 gallons are purchased then it's enough to cover the price of a Costco hot dog and Coke (with refill). Not bad at all.

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Additionally: While Costco seemingly doesn't make (much) money on gas, that doesn't mean that they're always cheaper.

Suppose I were making a Costco trip today and I also need to buy gas. I'd be heading to the Costco that has gas for $3.65 because that one is much closer for me.

But I can get gas for $3.62 right now at the station down the block from my house. There's no line there (there's never a line there), there's no membership proof to futz around with, and it's super easy to get in and out of.

Since I have enough easy information to make an informed decision, then: I can tell that the smart move is to plan on skipping whatever line may be present at Costco's gas station and just buy gas down the block. This will save me both time and money.

But tomorrow? Who knows. The situation may be different, so I may make a different decision.

I disagree. The prices still move with the price of oil. Their margins are just lower.