Ozzy Osbourne's band is hitting the road for The End farewell tour later this month (Jan15), and it has now emerged they will be offering gig-goers the chances to purchase a limited edition disc featuring unheard songs recorded during their sessions for hit album 13.

Bassist Geezer Butler explains the musicians wanted to find a way to share the unreleased tracks with fans.

"We went into the studio with 13 songs - which is why the album is called 13," he tells Billboard.com. "We thought we'd put out an album of 13 songs, but when we were in the studio we wrote another three songs, which brought it up to 16 and then we left it to (producer) Rick Rubin to pick which songs would go on the album, and to give it some light and shade he picked the eight songs that we (released) on the 13 album. We put a few songs on deluxe versions of the album and then we had the four left over, and we decided to do a gig-only CD."

Ozzy goes on to insist that the band's tour really will be its last as they are determined not to follow it up with any reunions.

"We're not gonna get back together in three years when we all run out of cash or whatever. I have no intention of that. This is really the end," he adds.

Black Sabbath's The End tour kicks off in Omaha, Nebraska on 20 January (16).