OZZY OSBOURNE and METALLICA are strongly rumored to be headlining this summer's Ozzfest, BLABBERMOUTH.NET can reveal. According to our sources, this year's edition of Ozzfest will consist of two separate two-day (Saturday/Sunday) events one of which will be held in Dallas in late July/early August, with OZZY headlining one day and METALLICA the other.The rumors come in the wake of this year's arrival of the metal-oriented Rockstar Energy Mayhem Tour, which will play 30 North American amphitheaters during July and August, the time when Ozzfest is traditionally making its rounds. Last year's Ozzfest offered free admission, with fans acquiring tickets mostly through sponsoring web sites. But the acts were not paid either, which resulted in a decidedly less than impressive main stage lineup. The Mayhem trek has already robbed Ozzfest of two potential main-stage heavyweights in DISTURBED and SLIPKNOT, with fan favorites DRAGONFORCE and MASTODON also taking part in the Mayhem tour. Kerrang.com reported last month that Ozzfest 2008 is strongly rumored to be coming to the UK with a one-off show at London's 02 Arena on July 19. OZZY OSBOURNE, who began a series of South American tour dates on March 30 with KORN and BLACK LABEL SOCIETY, looks set to headline the one-day extravaganza. Although promoters and agents involved with the show are remaining tight-lipped, Kerrang.com believes that other bands in the running are KILLSWITCH ENGAGE, ALICE IN CHAINS, SERJ TANKIAN, DIMMU BORGIR and LACUNA COIL.