iOS app developers who are looking to make big bucks on the App Store should consider using the in-app purchase model, according to a recently published study from Distimo. In-app purchases are a huge source of revenue, accounting for a whopping 72 percent of all App Store revenues.

That number has increased drastically from July of 2010, when only 28 percent of App Store revenues came from in-app purchases. What’s even more surprising is that only four percent of all apps are currently using the in-app purchase model.

This all points to a trend of freemium apps dominating the App Store. These, of course, are apps that are free to download and try out, but require an in-app purchase to supply full functionality. Freemium apps made up the majority of the revenue — 48 percent, or nearly half of all App Store earnings. Many of these apps are games, but comic apps are also starting to create an impact.

Distmo via TUAW