Phase two of Viacom's sale of Famous Music Publishing is underway. Industry sources estimate anywhere from a few to as many as 10 bidders offered enough money or other incentives during the initial phase to make the second round of the sale.

Although names have not been disclosed, it's likely that Sony/ATV Music, Warner Music Group, executive Charles Koppelman (backed by GTCR) and Strauss Zelnick's ZelnickMedia are among the second-round bidders.

During this phase, the parties will have an opportunity to conduct their due diligence for a closer look at the publishing catalog and financial information before making a firm offer. The first-round bids were based on the so-called book, which contains some financial information on Famous and its catalog, like revenue, net publisher's share (or NPS, the amount the publisher retains after paying songwriter and other third-party royalties) and the NPS for the top 200 songs over the last few years.

Viacom could not be immediately reached for comment.