When it comes to mobile payments, most people likely think of Apple (NASDAQ:AAPL) Pay or Alphabet's (NASDAQ:GOOG) (NASDAQ:GOOGL) Google Pay. However, a recent eMarketer study found that Starbucks (NASDAQ:SBUX) actually has the top proximity mobile payment app in the United States.

Chart showing the top four mobile proximity payment platforms in America.

Data source: eMarketer. Chart by author.

Moreover, eMarketer expects Starbucks to maintain that lead for the foreseeable future, with its 23.4 million users in 2018 rising to 29.8 million by 2022, compared to 27.5 million users on Apple Pay and 14.9 million on Google Pay.

eMarketer analyst Cindy Liu called the Starbucks app "one of the bigger success stories" in mobile payments, and attributes that success to its ability to tie payments to its loyalty rewards program. Liu noted that the value of paying with Starbucks' app was "clear and simple," since customers can "save time and money at the register, all while racking up rewards and special offers."

Many other companies, including Walmart and Target, integrated mobile payments into their own apps for similar reasons. It's clear that the battle in mobile payments won't simply be fought between the titans of tech -- it will also involve retailers' first-party apps.

Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool's board of directors. Leo Sun owns shares of Apple. The Motley Fool owns shares of and recommends Alphabet (A shares), Alphabet (C shares), Apple, and Starbucks. The Motley Fool has the following options: long January 2020 $150 calls on Apple and short January 2020 $155 calls on Apple. The Motley Fool has a disclosure policy.