U.S. retail giant Walmart said it would test a smaller-store format with the launch of Walmart Express -- stores that will often include gas stations.

The average Walmart superstore is about 184,000 square feet. The Walmart Express stores will average 15,000 square feet, MarketWatch reported.

Most Walmart Express stores will include a pharmacy and carry up to 13,000 items. The superstores sell about 100,000 items.

"Small stores are going to be a very good growth opportunity for us. They allow us to get access to places we aren't in. We have a pretty aggressive plan to build those," said Walmart U.S. chief executive Bill Simon.

Smaller stores allow Walmart to open outlets in smaller towns, such as Gentry, Ark., population 3,000, where one of the first two Walmart Express stores will be built.

While sales at Walmart's large stores have declined for eight consecutive quarters, stores at the 40,000-square-feet outlets called Walmart Market saw sales increase 4 percent in the first quarter of 2011.