Amazon.com on Thursday said Sony BMG Music Entertainment has agreed to sell music free of digital rights management technology on the online retailer's store. As a result, Amazon now has all four major record labels offering tunes on its DRM-free rival to Apple iTunes.

Sony BMG was the only major label not to offer DRM-free music, which is playable on any digital music device, including the market-leading Apple iPod, Microsoft Zune, and Creative Technology's Zen. Songs sold on Apple's and Microsoft's online stores contain DRM technology that prevent customers from easily playing purchased songs and movies on other vendors' devices.

Amazon does not offer software to organize music or burn tunes to CD, but purchased songs can be imported into other music-management applications, such as iTunes or Microsoft's Windows Media Player. Those programs could impose restrictions on use of imported tunes. Amazon provides an "MP3 Downloader" that downloads purchased tunes to iTunes or Windows Media Player libraries.

Amazon, which only sells DRM-free music, launched its music store in September after signing deals with Universal Music Group, part of Vivendi, and EMI. The retailer added Warner Music Group in December.

Besides offering a more flexible product, Amazon has also priced many of its songs below iTunes' standard price of 99 cents a track. About a third of the more than 3.1 million tracks offered on Amazon cost 89 cents. Most albums on Amazon are priced from $5.99 to $9.99. ITunes' typical album price is $9.99.

Besides the major labels, Amazon.com offers songs from more than 33,000 independent labels. What isn't clear from Amazon's statement is whether Sony BMG would offer its entire catalog or just a portion of it. Representatives with Amazon were not immediately available for comment.

Record companies have become more flexible in offering music on the Web as sales drop in an industry that is rapidly changing. Total album sales last year dropped nearly 15%, while rap album sales dropped a whopping 30%, according to the music industry news site Billboard.com.

The same report said that a 45% jump in digital track sales helped offset the loss.