The grocery wars are continuing to heat up, with Wal-Mart rolling out an online ordering pickup service at a handful of stores in the Twin Cities.

The largest grocer in the U.S. is launching the service on Wednesday at its stores in Cottage Grove, Oak Park Heights and Monticello. Its store in Maple Grove will get the service on Oct. 6.

Here's how it works: Customers access the service through Wal-Mart's grocery website or through its grocery mobile app. They select a local store that offers the service, pick out the items they want and then select a time — including later that same day — to pick up the orders. Then they drive up to the reserved orange parking spaces outside the store at an appointed time, where an employee retrieves the order and loads it into the car.

The idea is to save customers time as well as the potential hassle of venturing the shopping aisles with their children in tow.

"Our customers have told us that grocery pickup is a game changer," Katie Vitela, a Wal-Mart Minneapolis "market coach," said in a statement. "They are now able to complete their grocery shopping in a matter of minutes — between errands or on their way home from an after-school activity — without even unbuckling their seat belts."

There is a $30 minimum order requirement to use the service, which is free. More than 30,000 items are eligible, including some health and beauty products.

If a customer is unhappy with the freshness or quality of meat or produce chosen, he or she can bring back the item with the receipt and receive a refund.

Wal-Mart first began testing online grocery pickup in a handful of markets a few years ago.

This year, it has been rapidly expanding the service, which is now in more than 60 markets.

The retailer is also testing grocery home delivery in a couple of markets, and delivery through services like Uber, Lyft and Deliv.

Like most other major retailers, Wal-Mart is trying to keep up with Amazon and a host of other third-party services that have flooded the market with speedy delivery.

Minneapolis-based Target Corp. tested curbside pickup at several stores in California and New Jersey, but discontinued the service in June. Instead, it offers fee-based grocery home delivery through partner Instacart in a handful of markets, including the Twin Cities. Instacart also delivers from grocers such as Cub Foods and Whole Foods.

Last week, Google Express expanded its delivery service from retailers such as Whole Foods, Costco and Walgreens to the Twin Cities.

Kavita Kumar • 612-673-4113