Online spending has reached 5.5 percent of total grocery spending in the United States, with current shoppers at online grocers driving most of the growth by increasing order sizes. But a new report warns that even though supermarkets are in a “strong position” to serve this demand, Amazon is challenging by linking its grocery services to Prime discounts and investing in Whole Foods Market.

Grocery shoppers that use online services most actively increased their weekly online spending as a part of total weekly grocery spending from 28 percent in 2017 to 46 percent in 2018, according to the new study, published by Brick Meets Click and sponsored by Winooski, Vt.-based grocery ecommerce platform MyWebGrocer.

Additionally, with the nearly 30 percent of U.S. households that already grocery shop online, average order size increased $62 in 2017 to $69 in 2018, while both penetration and order frequency remained relatively flat. This suggests that current users will drive near-term growth.

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