Mobile commerce (mcommerce) is set to account for a significantly higher proportion of U.S. ecommerce in 2017, according to a new eMarketer report. This marks yet another year of huge year-over-year mcommerce growth, with the increase coming exclusively from smartphone users.

Overall ecommerce sales are expected to increase by 16% this year to $462 billion, or 9.2% of total U.S. retail sales. In terms of pure numbers, almost 150 million Americans are expected to shop online, an increase of 8% over 2016. Sales on mobile devices is set to grow by at least a third over last year to $157 billion, or 34% of all U.S. ecommerce.

While ecommerce overall is growing quickly, the penetration of ecommerce sales still varies dramatically by industry. In 2017, ecommerce is expected to be most prevalent within a handful of industries, specifically within apparel and consumer electronics, where ecommerce accounted for 18.7% and 16.7% of sales, respectively.

While mobile shopping isn’t new for online merchants, this report underlines the importance of maintaining a customer experience that is optimized for mobile users.