• Retailer will reach 40 percent of U.S. households in rollout
  • Service will compete against Amazon.com and Instacart

Walmart Inc. plans to expand its grocery home-delivery service to more than 100 metro areas this year, a sign its food fight with Amazon.com Inc. is heating up.

The service, currently in six cities, will roll out to more than 40 percent of U.S. households by the end of the year, the company said on Wednesday. Deliveries will be handled by Uber Technologies Inc. and other providers, and will carry a $9.95 service fee — with a $30 minimum purchase.

“We’re moving fast,” Tom Ward, Walmart’s vice president of digital operations, said in an interview. “We will be pretty aggressive with it.”

The move into home delivery is part of Walmart’s broader push to get more of its in-store shoppers to start buying online as well, where they typically spend twice as much. It also complements Walmart’s rollout of curbside grocery pickup, now available in 1,200 stores and coming to an additional 1,000 this year.

Walmart’s online business had been a bright spot for the chain, but it stumbled during the…