Instacart’s reach keeps expanding in the online grocery delivery business.

Supermarket chain Whole Foods on Thursday is expanding its delivery services with the mobile grocery shopping app Instacart to add an unspecified number of markets in addition to the 17 metro areas where Whole Foods customers have Instacart as a delivery option. Whole Foods first paired with Instacart in fall 2014.

Shoppers using Instacart can have groceries delivered in as little as an hour for $5.99, or within a two-hour window for $3.99. The only new markets named Thursday by Whole Foods and Instacart are Orange County, California, and Baltimore. Instacart currently serves a total of 18 markets throughout the U.S.

“Instacart and Whole Foods Market share a mutual commitment to providing our customers with the easiest and most seamless grocery shopping experience possible,” Instacart CEO Apoorva Mehta said. “We look forward to continuing to innovate with Whole Foods Market in the services that we can bring to users.”

Shoppers can order groceries from Whole Foods through Instacart’s mobile app or website in 17 markets including Chicago, Boston, San Francisco, and Washington, D.C., among others.

The arrangement with Instacart represents Whole Foods’ latest attempt to better reach shoppers on the go. In February, the chain said it would offer digital coupons through its mobile app.

Meanwhile, the market expansion with Whole Foods represents the latest win for Instacart. In December, Instacart announced it had expanded its grocery delivery partnership with Target Corp., No. 16 in the Internet Retailer 2015 Top 500 Guide, to include Chicago, San Francisco and Minneapolis.