Mobile is certainly the story over at Facebook (META -10.56%). And, fortunately for investors, the story is just beginning. All it takes is one chart to see that there's massive opportunity for Facebook to further monetize mobile:

Source: Data retrieved from Facebook SEC filings and investor slides.

With 71% of Facebook's monthly active users, or MAUs, on mobile, and just 41% of the social network's ad revenue coming from mobile, desktop users still account for the majority of ad revenue, even though they are the minority of MAUs.

Or another way to look at it: average revenue per user, or ARPU, on desktop is more than three times ARPU on mobile -- or $2.71 versus $0.84, respectively. If the past few quarters are any indication of the next few quarters, mobile ARPU should continue to sharply increase as Facebook continues to improve monetization opportunities on the mobile front.

Just how big is this opportunity? Even if Facebook doubled mobile ARPU, it would still be less than two-thirds desktop ARPU -- an achievement that certainly seems doable (maybe even within a year). With mobile revenue already accounting for 41% of total revenue, a doubling in mobile ARPU would have a huge impact on total revenue.

Rapid change
You can bet Facebook is well aware of the opportunity. In fact, in the last few months alone, Facebook has continued to rapidly implement new, major changes to support further mobile monetization. To illustrate, here are some of the major changes happening on mobile in just one area: mobile app adds.

On July 30, Facebook launched a feature that made it much easier to launch a mobile app ad. The feature allowed developers to build a mobile app ad by simply copying and pasting Google Play or Apple App Store app URLs into Facebook's Ads Create Tool. Then, on Oct. 1, Facebook really stepped up mobile app ads by allowing developers to create custom calls to action to encourage targeted users to use their apps. Powerful calls to action include:

  • Open link
  • Use app
  • Shop now
  • Play game
  • Book now
  • Listen now
  • Watch video

Facebook's official For Business blog explains further: "From these calls to action, businesses with deep links can send their existing customers directly into customized, specific locations within their apps, such as new content, sales or product promotions."

Customized app install add. Source: Facebook's official For Business blog.

Just yesterday, Facebook announced a plan to give developers even more customization by using app usage data. For instance, businesses can reach out to people who have downloaded their app but haven't used it recently.

Though mobile app ads are just one area of Facebook's mobile advertising, it shows just how fast the company is moving to maximize mobile monetization. Even more, ad products like this will actually do better on mobile devices than on desktops, allowing developers to display an ad for a compatible app on the right device to the right person.

Facebook's mobile story is just beginning. Investors should expect mobile ad revenue as a percentage of total ad revenue to continue to soar over the next several quarters. And, more important, mobile ARPU should continue to close its trailing gap behind desktop ARPU, significantly boosting the company's overall revenue.