Despite double-digit growth this year and next, Americans’ use of mobile wallets like Apple Pay, Android Pay and Samsung Pay, as well as branded apps that include mobile wallets like the Starbucks app, Walmart Pay and CVS Pay, will not reach mass adoption in the foreseeable future. This year, 38.4 million Americans 14 and over will have used their mobile phones to pay at the point of sale at least once in the preceding six months. That’s just 19.4% of US smartphone users. By 2020, that figure will grow to 33.1% of smartphone users.

“There are several reasons why US consumers aren’t yet making proximity payments en masse,” said eMarketer analyst Bryan Yeager. “There are still concerns about security, a patchwork of merchant acceptance, and a lack of perceived value in replacing the use of cash or card with the tap or scan of a smartphone. Nonetheless, eMarketer expects those issues to be addressed over the next several years, which will help propel growth.”

Proximity mobile payment users in the US skew young, with 11.9 million in the 25-to-34 age group in 2016—31.1% of the total. By 2020, this group will exceed 21 million, though its share will decrease to 27.8% as older consumers start paying at the point of sale with their phones. In 2017, close to 55% of all US proximity mobile payment users will be under 35, and more than three-quarters will be under 45.

This year, proximity mobile payment transactions will grow 183.3% to $27.67 billion. That figure will more than double next year to reach $62.49 billion. By 2020, proximity mobile payment transactions are expected to equal $314.13 billion.

“More than 90% of US retail sales ($4.45 trillion) will occur in traditional contexts like brick-and-mortar stores this year, which is where consumers primarily make proximity payments,” said Yeager. “Increasing acceptance of proximity payments at a wider array of merchants is pushing average spend via such methods higher, which helps explain why transaction value is growing far faster than the number of users.”

Mobile peer-to-peer (P2P) payment apps, such as Venmo and Square Cash, have been more widely adopted by US consumers than proximity mobile payments. eMarketer defines a mobile phone P2P payment as a transaction made between two individuals using a mobile phone as a payment method via mobile browsers and mobile apps. This year, 45.8 million US adults—nearly one-quarter of US adult smartphone users—will use a P2P payment app at least once per month. That figure will exceed one-third by 2018. The value of P2P mobile phone transactions will total $59.42 billion this year, with that figure growing to $92.10 billion by next year.