The voice shopping market is expected to grow from $2 billion today to $40 billion by 2022, according to a new survey of 1,500 owners of smart speaker like Google Home and Amazon Echo in the United States. The survey was conducted by OC&C Strategy Consultants in December 2017 and released today.

AI assistants are spreading to more devices in the home and to environments beyond the home like the car and workplace — so much so that, in the next four years, 55 percent of U.S. households are forecast to have a smart speaker, according to Juniper Research.

Grocery shopping is the most commonly used voice shopping category today, making up 20 percent of shopping among survey respondents. That’s not a complete surprise when you consider more than 50 percent of Amazon Echo speakers are used in the kitchen. Grocery is followed by entertainment (19 percent), electronics (17 percent), and clothing (8 percent).

A survey by Consumer Intelligence Research Partners last month found that Amazon has 69 percent of the U.S. smart speaker market, while Google brings in 31 percent. Though Amazon continued to outsell Google in the latter half of the year, Google did gain some ground as Home sales surged during the holiday season.

Google announced it’s sold millions of smart speakers in recent months, while Amazon said “tens of millions” of Alexa-enabled devices were sold and the Echo Dot was the best-selling product from any manufacturer in any category across all of Amazon this holiday season.

Players entering the smart speaker market this year include Apple, whose HomePod hit store shelves earlier this month; Samsung, which plans to release a smart speaker with Bixby inside in the second half of 2018; and potentially Facebook, which unnamed sources said plans to release a video chat device with voice control at F8 in May. Microsoft’s Cortana is also expected to make its way into additional devices this year following the release of the Harman Kardon Invoke in October.

Both Amazon’s Alexa and Google Assistant can make recommendations for voice shoppers today. These recommendations, like the kind Alexa draws from Amazon’s Choice products, will become even more important, the study says, since 85 percent of consumers pick the product Amazon suggests.

While Amazon draws from its marketplace, Google Assistant connects with Google Express, a service made available in the past year to get products from major retailers like Walmart, Home Depot, and Costco.

Amazon is reportedly in talks with brands like Procter & Gamble and Clorox to promote their products to Alexa users.