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| 'O Rom | Vacanze Romanes | Folk |
| Obelyskkh | Hymn to Pan | Folk Metal |
| Oblivious | Goons and Masters | Doom |
| Obrero | Mortui Vivos Docent | Doom |
| Obsession | Order of Chaos | Heavy Metal |
| Oceans Of Sadness | Mirror Palace | Prog Metal |
| Ochs Conny | Black Happy | Acoustic |
| Octavia Sperati | Winter Enclosure | Gothic |
| October Equus | October Equus | Prog |
| Odessa | The Final Day | Prog |
| Odessa | Stazione Getsemani XXV | Prog |
| Odin's Court | Deathanity | Prog Metal |
| Odin's Court | Human Life in Motion | Prog Metal |
| Odin's Court | Deathanity (R3) | Prog Metal |
| Odra Reg | God's Garden | Prog |
| Odyssice | Impression | Prog |
| Of The Wand and the Moon | Emptiness, Emptiness, Emptiness | Gothic |
| Officina F.lli Seravalle | Us Frais Cros Fris Fics Secs | Sperimentale |
| Officina F.lli Seravalle | Tajs! | Sperimentale |
| Officina F.lli Seravalle | Blecs | Sperimentale |
| Officina F.lli Seravalle | Ledros | Sperimentale |
| Ogogo + Linden | Ogogo + Linden | Avantgarde |
| Ogogo | Redux | Avantgarde |
| Ogogo | Lunar Surphase | Avantgarde |
| Ogre | Dawn of the Proto Man | Doom |
| Ogre | The Last Neanderthal | Doom |
| Oh. | Metallia | Prog |
| Ohgr | Devils In My Details | Electronic |
| Ohm | Ohm | Fusion |
| Ohm | Live on PKFK 90.7 FM | Fusion |
| O'Hora Tony | Escape Into the Sun | Hard Rock |
| Ojm | Volcano | Stoner |
| Okumoto Ryo | Coming Through | Prog |
| Old Bridge | Bless the Hell | Heavy Metal |
| Old Dead Tree | The Nameless Disease | Gothic Metal |
| Old Rock City Orchestra | Once Upon A Time | Psichedelic |
| Old Rock City Orchestra | Back To Earth | Psichedelic |
| Ole Lukkoye | Petroglyphs | World Music |
| Ole Lukkoye | Dyatly | World Music |
| Oliver Dawson Saxon | Motorbiker | Heavy Metal |
| Oliver Dawson Saxon | Blood and Thunder Live |
Heavy Metal |
| Oliver Wakeman Band | Coming to Town | Pomp |
| Olivieri Luca | La Quarta Dimensione | World Ambient |
| Olivieri Luca | La Saggezza delle Nuvole | Electronic |
| Olivieri Raffaele | Improvvisamente la Luna | Jazz |
| Olson Mark | The Salvation Blues | Roots Rock |
| Omasphère | Prélude | World Music |
| Omega | The Prophet | Prog Metal |
| Omega Lithium | Dreams in Formaline | Gothic Metal |
| Omni | El Vals de los Duendes | Prog |
| On A Bridge Of Dust | Facing the Opposite | Prog Metal |
| On The Moon | Episodio 1 | Alternative |
| Oneira | Natural Prestige | Prog Metal |
| Oneira | Hyoerconscious | Prog Metal |
| Oniric | Suggestioni | Gothic |
| Onze H30 | Onze H30 | Rock |
| Oophoi & Louisa John Kroll | I Hear the Water Dreming | Electronic |
| Open Up | Open Up | AOR |
| Opera Multi Steel | La Légende Dorée | Cold Wave |
| Opera Noire | Bad Intent | Gothic |
| Opposition Of One | I Try to Understand This | Metal Core |
| Optimystical | Optimystical | AOR |
| Opus Est | Opus I | Prog |
| Orchestra Panica | Journey to Devotion | Sperimentale |
| Orchestre Celesti | Compi la Tua Magia | Prog |
| Orchestre Celesti | Black and Red | Prog |
| Orchestre Celesti | Transition of Power | Prog |
| Orchestre Celesti | Quattro | Prog |
| Ordinary Brainwash | ME 2.0 | Prog |
| Oresund Space Collective | Oresund Space Collective | Space Rock |
| Oresund Space Collective | It's All About Delay | Space Rock |
| Oresund Space Collective | The Black Tomato | Space Rock |
| Oresund Space Collective | Good Planets Are Hard To Find | Space Rock |
| Oresund Space Collective | Dead Man in Space | Space Rock |
| Oresund Space Collective | Different Creatures | Space Rock |
| Orford Martin | The Old Road | Rock |
| Organima | Il Mondo | Nu Metal |
| Orghanon | Figures in Slow Motion | Electronic |
| O.R.K. | Ramagehead | Prog |
| Orme, Le | Live in Pennsylvania | Prog |
| Orme, Le | La Via della Seta | Prog |
| Orne | The Conjuration By the Fire | Dark Rock |
| Orne | The Tree of Life | Prog |
| Orplid | Greifenherz | Neo Folk |
| Osada Vida | Three Seats Behind a Triangle | Prog |
| Osada Vida | The Body Parts Party | Prog |
| Osada Vida | Uninvited Dreams | Prog |
| Osada Vida | Where the Devils Live (dvd) | Prog |
| Osada Vida | Particles | Prog |
| Osada Vida | The After-Effect | Prog |
| Osanna | Tempo | Prog |
| Osi | Free | Prog Metal |
| Osi | Blood | Prog Metal |
| Osiris | Beyond Control | Prog |
| Osiris | Visions From the Past | Prog |
| Osselico | Osselico | Dark Rock |
| Ossimoro | Corvi Nel Cielo Spento | Stoner |
| Osta Love | Good Morning Dystopia | Prog |
| Ostinati | Stone Wall | Jazz |
| Oteme | Il Giardino Disincantato | Prog |
| Oteme | L'Agguato, L'Abbandono, Il Mutamento | Prog |
| Other, the | We Are Who We Eat | Horror Punk |
| Other, the | New Blood | Horror Punk |
| Ottone Pesante | Doomood | Brass Metal |
| OTR | Mamonama | Hard Rock |
| O-U | O-U | Prog |
| OU | II: Frailty | Prog Metal |
| Outer Limits | Stromatolite | Prog |
| Outgunned | Vol.I: Answering the Censeless Need | Prog Metal |
| Outloud | Let's Get Serious | Heavy Rock |
| Outopsya | Sum | Prog Metal |
| Outopsya | Fake | Prog Metal |
| Over Jazz Duo | Beautiful Love | Jazz |
| Over The Edge | Over The Edge | AOR |
| Overlogic | From Where? | Electronic |
| Overdrive | Angelmaker | Heavy Metal |
| Overfaith | Our Regretless Awakening | Heavy Metal |
| Overhead | Metaepitome | Prog |
| Overhead | And We're Not Here After All | Prog |
| Overhead | Of Sun and Moon | Prog |
| Overland | Epic | AOR |
| Overunit Machine | Antropophobia | Crossover |
| Owens Tim Ripper | Play My Game | Heavy Metal |
| Ox | When Things Come Easy | Rock |
| Oxley Pete Meier Nicolas | Chasing Tales | Acoustic |
| Oz Noy | Ha! | Fusion |
| Ozark Mountain Daredevils | Our Most Dangerous Stunts | Country |
| Ozric Tentacles | Spirals in Hyperspace | Prog |
| Ozric Tentacles | The Floor's Too Far Away | Prog |