Wal-Mart

(WMT) - Get Report

said same-store sales at its main discount chain were below plan again last week and reiterated that same-store sales growth for all of September will most likely be at the low end of expectations.

It was the second week in a row of below-plan sales at the company's Wal-Mart unit, following two weeks of above-plan results. Same-store sales at

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, Wal-Mart's warehouse division, were above plan, the company said Monday in a recorded message for investors. Same-store sales are sales at stores open at least a year.

The world's biggest retailer said high gasoline prices and fears about higher heating costs for the coming winter may have cut down on traffic to its Wal-Mart stores, whose lower-income customers are more sensitive to those costs. Growth in September same-store sales will likely be at the low end of the company's 4% to 6% expectations due to a calendar quirk, the company said. Most retailers report same-store sales on Thursday, Oct. 5.

Wal-Mart's shares fell 88 cents, or 1.7%, to $49.63.