Amazon.com Inc. today launched a $6 million royalty fund designed to encourage use of its Kindle e-book readers and boost interest in its Prime free shipping program. The royalties will go to independent authors and publishers based on the popularity of their titles, as part of a program that Amazon dubs KDP Select (the KDP stands for Kindle Direct Publishing).

Those authors and publishers must put their titles exclusively into the Kindle store for at least 90 days, says Amazon, No. 1 in the Internet Retailer Top 500 Guide. Those books then are eligible for inclusion in the Kindle Owners’ Lending Library—Kindle owners who sign up for the $79-a-year Prime free shipping program can borrow up to a book a month for download to their Kindle devices.

Amazon says it will base monthly royalties on a specific book’s share of the number of books borrowed through the KDP Select program. For instance, Amazon gave this example: If the number of borrowed books in KDP Select were to hit 100,000 in a given month, and consumers borrowed a particular book 7,500 times, that author would earn $7,500 in royalties under the program. Amazon says the monthly royalty fund could pay out as much as $500,000 for December. “By choosing KDP Select, independent authors and publishers have an opportunity to make money in a whole new way and reach the growing audience of Amazon Prime members,” says Russ Grandinetti, vice president of Kindle Content. “A short 90-day commitment allows authors and publishers to experiment at very low risk.”

Amazon says that 31 of the top 50 independent Kindle authors have already enrolled in the program, which includes at least 129 titles. Such authors include J. Carson Black, Gemma Halliday, J.A. Konrath, B.V. Larson, C.J. Lyons, Scott Nicholson, Julie Ortolon, Theresa Ragan, J.R. Rain and Patricia Ryan.