Wal-Mart is stirring the pot and defending its fast-growing online grocery business in the Dallas area by partnering with Uber to make home deliveries.

The test with Uber started last year in Phoenix and expanded Monday to Dallas and two Florida markets, Orlando and Tampa.

Eight stores in the Dallas area will fill the orders, and Wal-Mart's personal shoppers will pack groceries into "special cold pack bags," said Wal-Mart spokeswoman Anne Hatfield.

Customers will know if the service is available in their ZIP code if they're offered the home delivery option at checkout. The fee is a flat $9.95 and charged by Wal-Mart, who pays Uber. Same-day orders must be made by 1 p.m., and customers choose one-hour delivery time slots.

The announcement comes as discount grocery rival Aldi said last week that its customers can chose to order online through Instacart later this month. All of a sudden, local customers have more than half a dozen options for completing the family's grocery shopping without leaving the house.

Dallas-Fort Worth is Wal-Mart's largest online grocery market. It has more than 53 stores equipped to handle online orders that the customer picks up at a designated curbside area. Two more stores in Anna and Fort Worth are being added in September. There is no fee for that service.

Kroger has a similar service, but also partners with Instacart for home deliveries. Other local Instacart partners are Whole Foods, Central Market, Tom Thumb, Costco and Natural Grocers. Amazon Prime Now offers perishable groceries in Dallas through an agreement with Sprouts.

Last week, Wal-Mart reported a 1.8 percent second-quarter sales increase on the strength of its online business and groceries. It was the 12th consecutive rise in same-stores sales and included a 1.3 percent increase in foot traffic.

Wal-Mart has multiple tests underway to get both general merchandise and groceries to customers who prefer to shop online as it's locked in a battle with Amazon.com.

As the largest U.S. grocery retailer, Wal-Mart has a huge head start over Amazon in the food business. Amazon's pending $13.7 billion acquisition of Austin-based Whole Foods Market will give it a lift.

Wal-Mart is still calling the Uber partnership a test and will be collecting feedback from customers, Hatfield said. "We want to make sure that we know it's working for customers."

Wal-Mart has several online tests and new ways to get online orders to customers. This summer in Dallas, it started installing big orange towers that are similar to a vending machine and dispense small online orders of general merchandise. In New Jersey, it's testing deliveries of general merchandise with Wal-Mart store employees who want to make extra money on their way home from work.

In Denver and San Jose, Wal-Mart has been using its own trucks for online groceries since 2013. In Oklahoma City, it has a 24-hour automated grocery kiosk for online orders. The 20-by-80-foot building is in the parking lot of a Wal-Mart Supercenter in Oklahoma City.

"We're trying a lot of different tests," Hatfield said.

In Dallas, Uber drivers are used to delivering restaurant food. The people-moving app morphed into a restaurant delivery service more than a year ago. UberEats is McDonald's official delivery service in Dallas.

This week, Wal-Mart will have cars driving around Dallas with a fake, giant orange displayed on the roof to call attention to the service and be part of a social media contest. D-FW is the only market with the vehicle promotion.

"Orange you glad we're delivering?" reads the shrink-wrapped vehicle.

Wal-Mart stores fulfilling online orders:

Garland: 5302 N. Garland Ave.

Irving: 1635 Market Place Blvd.

Lewisville: 190 E Round Grove Road

Murphy: 115 W FM 544, Murphy

Plano: 6001 North Central Expy.

Plano: 425 Coit Road

Rowlett: 2501 Lakeview Pkwy.

The Colony: 4691 State Highway 121

Twitter: @MariaHalkias