While the bulk of attention on Apple Pay and Android Pay has been directed at their in-store contactless payment capabilities, in-app and browser-based online payments could be the source of most of their growth in the next few years, according to a new report. By 2018, the value of online payments made through apps and on e-commerce Websites via Apple Pay and Android Pay will increase nearly 15 times. In its new report, Mobile & Online Remote Payments for Digital & Physical Goods: Opportunities & Forecasts 2016-2021 , Juniper Research said consumers’ online spend using the two mobile wallets will surge from $540 million this year to $8 billion in two years. The U.K.-based consultancy points to the proliferation of mobile commerce and the importance of reducing friction during mobile transactions.

“It is clear that even in markets where PCs and laptops have a high installed base that the smartphone is playing an increasingly important role where remote goods purchases are concerned,” said Steffen Sorrell, the report’s author. “For merchants, this means that the buyer experience must be made as frictionless as possible—from product search and discovery to purchase.”

The report noted that, even combined, Apple Pay and Android Pay have a long way to go to overtake PayPal as the online, digital wallet leader. And, while rival Visa Checkout also has a head start, having launched last year, once the OS-based wallets offer browser-based payments, Sorrell told CardNotPresent.com they could quickly eclipse other payment methods.

“Apple Pay is expected to launch Web payments with online merchants by the end of this year; we anticipate that Android Pay will adopt the same approach once the service has become more widespread across markets,” he noted. “Once these services are available across app and Web platforms, consumer expectation alongside merchants’ desire to reduce buyer friction will mean that integration with Web stores is likely to be quite rapid, as long as there are no complex hurdles to overcome. Visa Checkout requires a username and password; while this is a simpler mechanism than entering long card numbers, the increasing proportion of consumers spending on mobile will mean that the most convenient payment mechanisms are likely to win out. At present, Apple Pay and Android Pay are near-seamless payment services due to biometric/PIN authentication.”