Walmart said Thursday it will be expanding a new "unlimited" grocery delivery service, which costs users $98 annually, to 1,400 stores this fall.

The biggest retailer in the world had earlier this year been testing what it calls Delivery Unlimited in four markets — Houston, Miami, Salt Lake City and Tampa. As part of the nationwide rollout, it said the service will be available in 200 metro areas where it already has regular grocery delivery, reaching more than 50% of the U.S. population, by the end of the year.

Walmart's Delivery Unlimited gives shoppers the option to pay either $98 per year or $12.95 per month to receive unlimited grocery delivery orders to their homes. Typically, on an order-by-order basis, delivery would cost an additional $9.99. In addition to fresh produce, meat and bakery items, some general merchandise is offered under the new unlimited service, the company said.

"We've been investing in our online grocery business by quickly expanding our Grocery Pickup and Delivery services. Delivery Unlimited is the next step in that journey," Tom Ward, senior vice president of Walmart's digital operations in the U.S., said in a statement. "By pairing our size and scale and these services we're making Walmart the easiest place to shop."