Known for its supercenters, Wal-Mart Stores Inc. is quietly testing a format less than a tenth the size and may make the smaller “Express” format stores a more important part of the company’s portfolio in coming years.

The Bentonville, Ark.-based retailer has 10 Walmart Express stores in test phase, with three in Arkansas, two in Illinois and the remainder in North Carolina, said spokeswoman Deisha Galberth Barnett. The first of these stores opened in 2011 and the most recent in May.

The format has been more successful than anticipated. Bill Simon, chief executive officer of U.S. operations, reportedly said recently the company plans to reduce construction and distribution costs, and determine how densely they can be built in a market.

Walmart Express stores run about 15,000 square feet and offer “essential needs, including grocery, consumables and limited general merchandise.”

Galbert Barrett did not specify the size of produce departments, or what types of produce they offer, but an article in the Raleigh, N.C. News & Observer said the Walmart is promoting local produce sold in the stores, including North Carolina sweet potatoes.

This concept could work for Wal-Mart, said retail analyst David Livingston.

“(They’re) getting into smaller markets with enough potential to make it work with little or no competition, or completely ineffectual competition,” he said.

Supercenters remain the retailer’s focus, Galberth Barrett said.

“We expect to test, learn and refine these stores before we decide to roll out the smaller format on a large scale,” she said. “We continue to see tremendous growth opportunities and remain committed to growing through new supercenters, as well as small formats. Supercenters remain the priority and the best format for capturing market share.”