Analysts were estimating a 3.1 percent rise in August sales at stores open at least a year at the retailers tracked by Thomson Reuters I/B/E/S. Most, including Costco Wholesale and Buckle, beat expectations for the month on Thursday, while Victoria's Secret parent L Brands Inc missed estimates.
The Standard & Poor's Retail Index was up 0.6 percent on Thursday morning, outpacing a 0.3 percent gain for the broad S&P 500.
Same-store sales are an important measure of a retailer's performance because they strip out the effects of store openings and closings.
Fewer than a dozen U.S. retailers report monthly sales, down from a peak of 68 in 2006. In the years since, big names such as Macy's, Wal-Mart Stores, and Best Buy have dropped out of the same-store sales index.
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Mall-based apparel chain Cato Corp.'s same-store sales fell 2 percent, while analysts expected a 3 percent drop.
"We remain cautious in regard to the remainder of the year," Chief Executive Officer John Cato said in a statement.
Buckle, which caters to teenagers, reported a 1 percent rise, beating estimates of a 0.4 percent increase.
Costco's same-store sales, including those of gasoline, rose 4 percent, just beating analysts' expectations of a 3.8 percent gain. Demand was strong for health and beauty aids and food, but weak for electronics, the largest U.S. warehouse club chain said.
Stein Mart also topped same-store sales forecasts for the month, reporting a 3.8 percent rise on strong demand for everything from linens to women's dresses.
Walgreen, the largest U.S. drugstore operator, reported a 4.8 percent increase, while analysts had expected only a 2.8 percent rise.