Amazon today announced its Amazon Mobile Ads API service for mobile developers to monetize their apps.

Amazon is entering a crowded mobile ad network market filled with the likes of Google AdMob, Millennial Media and InMobi. Even Facebook seemed poised to get into this business at one point last year before it ended its test after a few months.

Amazon did not share what cut of ad fees it offers developers, but says its service offers a “competitive eCPM.” According to the company’s publisher agreement, the portion of the advertising fees that a developer will receive “may be adjusted depending on a variety of factors, such as the quality of your inventory or deductions for various expenses.” Ads will come with mobile-optimized display ads from Amazon itself and other “top” brands, the company says.

Amazon’s mobile ads API offers ads in two different flavors. First is the “floating ad,” which acts like a typical mobile banner ad that floats at the bottom of the screen. Second, is the “simple ad,” which is a rich media expandable banner ad such as a video ad.

For now, the API is in beta and only available for U.S. users and apps for the Kindle Fire, Kindle Fire HD and other Android smartphones and tablets. Note that for the API to work in a developer’s app, the app has to be available for download on Google Play as well as on the Amazon Appstore for Android.

Developers interested Amazon’s mobile ads API can head here for more information and to download the API.