While lower- and middle-income shoppers increased their spending at Wal-Mart when the economy started to soften, the report finds that the bigger change has been upper-income consumers who have flocked to Wal-Mart in the last six months, as gas prices soared. The report says that the combination of $4 prescriptions, competitive prices in key food categories, and wider product assortments are responsible for the shift.

"Low prices and one-stop shopping have proven to be an incredibly powerful combination at a time when consumers are forced to strategize to maximize gas usage and stretch budgets as far as they will go," the company says in its release. "Wal-Mart is exceptionally well positioned for growth."

Of course, Wal-Mart isn't the only store benefiting from this shift in shopping patterns, as consumers balance the need to save money on groceries with the pressure to use less gas. The result is fewer, larger trips, and all supercenters have been capturing share in all income and lifestage segments, as well as attracting those who shop heavily in competing channels.

In the 12 months ended in June, IRI says three-quarters of all shoppers typically visit five or more channels for consumer products. But while 50% say they are often shopping around for better deals, only 10% are now willing to drive further to get them. While grocery stores still lead the way with a 55.2% share of shoppers, that represents a decline of 0.2%. Supercenters are next, with a 15.1% share--a gain of 1.4%.

The report finds that grocery stores have lost ground in the fresh/perishable, frozen and center store categories, including high-demand meal ingredient and meal component foods. And Wal-Mart--despite a decline in share its private-label goods--has made considerable gains in meal ingredients, meal components and convenience meals.