Walmart, Sam’s Club and H-E-B were named the top-performing U.S. grocery retailers for in-store pickup, curbside pickup and home delivery, respectively, in a new study by global research firm Ipsos.

Ipsos said its inaugural E-Commerce Experience Report gauges buy-online-pickup-in-store (BOPIS), curbside and delivery services of major retail brands. The two-pronged study first surveyed 2,000 U.S. consumers about their usage, attitudes and perceptions of retailer pickup and delivery offerings, and then researchers conducted thousands of mystery shopping trips (150 per brand) that evaluated the pickup and delivery services of national and regional retailers.

The mystery shoppers audited retailers’ pickup and delivery services through all phases of the process, New York-based Ipsos noted. Key performance indicators ranged from account creation, ordering and the actual pickup/delivery to ease of use, user experience and likelihood to recommend service.

In grocery retail, Walmart performed the strongest across all measured attributes for BOPIS service. Ipsos’ E-Commerce Experience Report said Walmart excelled, in particular, at posting visible signage that steered consumers to the grocery pickup area, which was found in 86% of the stores visited. Rival Target also performed “exceptionally well” in BOPIS, with the retailer having grocery orders ready when promised at 98% of visited locations.Walmart subsidiary Sam’s Club came in at No. 1 in curbside pickup grocery service. Ipsos said the warehouse club chain exhibited a “near perfect performance,” especially in allocating dedicated curbside parking spaces at 100% of stores audited. Supermarket giant Kroger was a close second in curbside service, performing well in categories that customers noted caring about most and having orders ready when promised at 97% of locations.

In grocery delivery, Ipsos ranked H-E-B first in service, noting the Texas chain’s 99% accuracy rate on delivery orders. Amazon’s Whole Foods Market also performed well on that attribute, with 95% order accuracy in the mystery shopping trips. The study, too, cited a strong delivery showing by discount grocer Aldi, namely in providing delivery notifications on 95% of orders. Aldi’s same-day delivery service is provided by Instacart.Ipsos spotlighted areas where grocery and other retailers could improve to ensure a positive, end-to-end e-commerce experience for customers, given the still “tremendous growth opportunity” in BOPIS, curbside and delivery.All customers polled said clear communication is key to pickup and delivery, yet more than a quarter of shoppers see room for improvement in communication for these services, the study found.In pickup specifically, retailers need to offer dedicated curbside parking sites and put up prominent signage to make it easy for customers, Ipsos said. Among the mystery shopping trips, 27% of BOPIS locations were poorly marked or difficult to find. Order accuracy is paramount for delivery, but 9% of consumers surveyed said their order wasn’t accurate.