Amazon.com Inc. is planning to open a software-applications store for smartphones running Google Inc.'s Android operating system, putting it in direct competition with Google's own marketplace as well as Apple Inc.'s App Store.

According to an Amazon document for developers that was viewed by The Wall Street Journal, Amazon would take a 30% cut of sales, with the developers keeping the rest. The document includes a stipulation that the apps can't be offered at a lower price anywhere else.

The revenue-share split is consistent with other app stores, such as Apple's industry-leading iTunes store, which sells apps for iPhones and iPads.

Amazon is asking developers to commit to putting up apps that are already publicly available within two weeks of accepting its terms of agreement, according to the document. Future apps must also be delivered within two weeks of the apps' initial availability on any similar marketplace.

Some developers who have been approached by Amazon about the new app store said they haven't been told what the store will be called or when it might open.

An Amazon spokeswoman said "we don't comment on rumors and speculation." Google didn't immediately respond to a request for comment.

Amazon's app-store plan was reported earlier by the TechCrunch website.

Android-based phones have been one of the fastest growing categories of smartphones as mobile operators that don't carry the iPhone like Verizon Wireless have heavily promoted the devices made by companies like Motorola Inc. and HTC Corp.

In the U.S., Android's market share has climbed to 19.6% of smartphones at the end of August from 2.5% a year earlier, according to comScore. In comparison, the iPhone's market share was 24.2% at the end of August.

In opening its own app store, Amazon will be pitting itself against a formidable rival. Google, which created the Android operating system, runs its own marketplace called Android Market, which already has 80,000 apps and is the second largest after Apple's App Store, which has 250,000 apps.

But while the two-year old Android Market is considered to be successful, developers believe there is a window of opportunity for Amazon to offer a more organized alternative marketplace.

Amazon isn't the only company eying a potential app store for the fast-growing Android smartphone category. Last month, Verizon Wireless rolled out a curated app store of its own, dubbed V CAST Apps, as a tab within Google's existing Android Marketplace.

A spokeswoman for Verizon said "choice is always good for consumers."