Wal-Mart Stores, Inc. (WMT) might truly be the cheapest retailer.

The supermarket chain now beats Dollar General Corp. (DG) in pricing, according to a Gordon Haskett Research Advisors in a note published Monday, Oct. 16.

Comparing Dollar General, Family Dollar Stores Inc. (FDO)  and Walmart based on 53 items in Houston, Atlanta, Chicago and Central New Jersey, analyst Charles Grom and his team found that Walmart is now cheaper than both; Walmart was already leading Family Dollar as of July, his previous study that month found.

"For the first time since we started this study back in March, our September results show that Walmart is now priced below Dollar General," Grom wrote. "To this end, the Dollar General basket is priced at a 90 basis-point premium to Walmart as compared to a 200 basis-point discount just two months earlier in July."

In March, Walmart announced a new price-comparison test in more than 1,000 stores to bring down its prices. "We're always working to deliver lower prices to our customers," spokesman Lorenzo Lopez told TheStreet then.

Walmart made notable gains on food, Grom found. In July, food at Dollar General was priced at a 1.1% to Walmart. But in September, that figure jumped to 4.8%. The Arkansas-based retailer also widened its price margin on Kroger Company (KR) , Target Corp. (TGT)   and Albertsons, as well as its subsidiary Randall's Food Markets, Inc. Albertsons is privately held.  

Amazon.com, Inc. (AMZN) is also making progress on the price front. Amazon Fresh has tightened its gap on Walmart prices for five consecutive months, according to the Gordon Haskett report.

Meanwhile, Target isn't making any leeway in its investment to lower prices. Based on Grom's repeated price study of the same 73 items, he found that Target lowered list prices on about six items per market in August and September. The total of those rang up a higher price, expanding Walmart's lead over Target by 5.6%.

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