NEW YORK (AP) - Walmart is rolling out an unlimited grocery delivery subscription service this fall as it races to gain an advantage in the competitive fresh food business.

The service will charge an annual membership fee of $98 for subscribers to access unlimited same-day delivery, which will be offered in 1,400 stores in 200 markets. By year-end, it will extend to a total of 1,600 stores - or more than 50 percent of the country.

The move allows the nation's largest grocer to further tap into time-starved shoppers looking for convenience at a time when Walmart is locked in an arms race with Amazon and others to expand fresh-food delivery.

About two years ago, Amazon purchased Whole Food Market Inc. and is now is offering same-day grocery delivery in various cities.