Discount chains registered a 3 percent same-store sales gain, while wholesale clubs posted a 9.2 percent gain. Meanwhile, same-store sales at apparel chain stores fell 1.4 percent, according to the ICSC tally.

Except for Wal-Mart, whose shares rose 33 cents to $57.16, investors pushed many retailers' shares down Thursday. Penney's stock fell 2.41 percent, and Costco's shares lost more than 1 percent.

Janet Hoffman, managing partner of the North American retail division of Accenture was surprised to see that the April reports showed "a broader base of customers" switching to outlets.

A limping economy, soaring food and gas prices, limited credit, slumping home prices and worries about jobs continue to unnerve shoppers. Americans are gloomier about the economy than just before the U.S. invasion of Iraq in March 2003, according to a recent survey by the Conference Board, a business-backed research group

They're even taking on more debt to pay for food and fuel. The Federal Reserve reported Wednesday that consumer borrowing, particularly on credit cards and auto loans, rose in March at the fastest pace in four months, more than double the increase of the previous month.

Eduardo Castro-Wright, Wal-Mart Stores U.S. president and CEO, said in a statement that the "economy continues to get tougher," and customers increasingly are unable to stretch their dollars to the next pay day.

But that's also been a boon for discounter Wal-Mart, which has spruced up its stores and merchandise.

Wal-Mart reported a 3.2 percent gain in same-store sales. Analysts polled by Thomson Financial expected a 2.1 percent gain. Including fuel, same-store sales climbed 3.8 percent.

Its business was fueled by strong sales in grocery and health items, and by entertainment products like flat-panel TVs and video games. The company said apparel sales continued to recover, despite cold weather, but home-furnishings sales were weak.

Costco's 8 percent increase surpassed the 6.1 percent estimate, helped by higher gas prices. Excluding fuel, same-store sales rose a solid 5 percent as shoppers were attracted to buying merchandise in bulk.

Meanwhile, many mall-based apparel chains struggled. Among department stores, Penney reported a 1.7 percent decline in same-store sales, though that was better than the 4.6 percent decline analysts expected. Nordstrom Inc. posted a 3.8 percent drop in same-store sales, more than double the decline that Wall Street expected.