What happens when someone features guitar tabs on a Web site so musicians can learn to play their favorite songs? The posting is probably copyright infringement since publishers have licensed very few guitar tab sites. But publishers are facing even more pressing questions than whether they should sue the unauthorized sites: What is the best business model to compete with the free, unauthorized sites, and do current publishing contracts even cover the necessary rights to post tabs to the authorized sites?

The sale of print versions of guitar tabs is a multimillion-dollar business. Although publishers' revenue is confidential, a source with a print publisher crunched some numbers for me based on information from a NAMM report, the company's own revenue and the source's estimate of competitors' revenue.

According to a NAMM report, the North American print music market generated $539 million in retail sales in 2006. My source estimates that about 48% of that amount ($258.7 million) was related to songs in about 2.7 million songbooks. About 16% of the song portion of the revenue was likely attributable to guitar tabs, thereby generating roughly $41.4 million in retail revenue from about 40 million individual guitar tabs. With wholesale prices typically 45%-50% of the retail price, print publishers likely received $18.6 million-$20.7 million in 2006 from print guitar tabs, which they then shared with songwriters and their publishers.

Currently, only three commercial guitar tab sites appear to be authorized by a large number of publishers. Each sells tabs as digital sheet music: FreeHand Music (FreeHand Systems), Musicnotes and SheetMusicDirect (Hal Leonard and Music Sales U.K.). Meanwhile, sites that may contain unlicensed tabs keep growing. From July 2006 to July 2007, unique monthly visitors grew for ultimate-guitar.com from 1.4 million to 2.4 million, and for 911tabs.com from 473,000 to 1.1 million, according to comScore Media Metrix.

In an attempt to compete with the free sites, Musicnotes acquired a previously unlicensed site, MXTabs.net, with plans to license the site's database of tabs and add others, offer them for free and share ad revenue with publishers. Among the publishers that licensed rights for the site were BMG Music Publishing, Famous Music, Bug Music and peermusic.

But when Musicnotes made a deal with the Harry Fox Agency in May so that publishers could opt in to the licensing deal for MXTabs, Hal Leonard reacted negatively. It e-mailed some publishers to urge them to think carefully before licensing the "free" business model, which may include amateur (i.e., not necessarily accurate) guitar transcriptions of songs. Musicnotes posted the letter and its reply on the MXTabs site, which has not yet launched its service.

It's unclear whether the reaction to the dispute is holding up the site. But the debate is unlikely to be resolved soon. It boils down to two questions: In light of all the illegal sites, should tabs be offered for free on ad-supported sites even though "free" may feed into a consumer demand for more free music, thus devaluing music? Or should legal action shutting down unauthorized sites and educational efforts be the strategy for publishers while building per-download or per-use sites for tabs?