"O"

OPETH picks 

Mikael Åkerfeldt, Fredrik Åkesson

OZZY OSBOURNE picks

Zakk Wylde, Mike Inez, Robert Trujillo, 

Adam Wakeman, Blasko, Joe Holmes, Gus G

OFFSPRING picks 

Dexter Holland, Noodles, Greg K, 

OBITUARY picks 

Terry Butler, Ralph Santolla, Frank Watkins, Ken Andrew

Overkill picks

D. D. Verni, Dave Linsk, Derek Tailer,

Merritt Gant, Rob Cannavino,

Joe Comeau, Bobby Gustafson