Question:  Since Walmart and Costco now sell gas at their stores, is the gas included in their "retail sales"?

If so, wouldn't the higher gas prices increase their retail sales?

That seems to have worked for CostCo.

However, it's becoming more and more difficult for independent retailers to get good prices on gasoline.  The gas stations that are connected with oil companies have a pricing advantage, and even large independents like Wal-Mart are hurting.

Interesting that same store sales are not keeping up with inflation, even after the added "juice" from the fueling stations. Even more interesting is that Wal-Mart same store sales track (at least by my recollection) the increase in non-salary wages. These increased much mre rapidly in the Clinton years, which accounts for most of Wal-Mart's growth.
I don't know about the rest of the nation, but in the Southeast, the gasoline concession at Wal Mart is contracted out to Murphy Oil Company. I don't know what the terms of the contract are, I am sure Wal Mart gets a share of the sales. But basically the company selling the gasoline is Murphy.