| Artist | Title | Release Year | Length | Genre | Label | Format | Tracks |
|---|---|---|---|---|---|---|---|
| O Bando | O Bando | 1969 | 34:55 | Rock | Shadoks Music | CD | 11 |
| Oakley Hall | Gypsum Strings | 2006 | 44:02 | Rock | Brah Records | CD | 9 |
| Oakley Hall | I'll Follow You | 2007 | 49:27 | Rock | Merge Records | CD | 12 |
| Oak's Mary | Car Wash | 2006 | 45:39 | Rock | Desert Fox Records | CD | 10 |
| Oak's Mary | Mathilda | 2009 | 50:06 | Rock | Desert Fox Records | CD | 11 |
| Obiat | Eye Tree Pi | 2009 | 57:34 | Metal | Small Stone Recordings | CD | 7 |
| Oblivious | Goons And Masters | 2009 | 50:01 | Rock | Transubstans Records | CD | 10 |
| The Obsessed | The Obsessed | 1990 | 32:32 | Metal | Hellhound Records | CD | 9 |
| The Obsessed | Lunar Womb | 1991 | 40:56 | Rock | Hellhound Records | CD | 12 |
| The Obsessed | To Protect And To Serve | 1994 | 05:59 | Rock | Columbia | CD | 2 |
| The Obsessed | Incarnate | 1999 | 48:07 | Metal | Southern Lord Recordings | CD | 13 |
| Obskuria | Discovery Of Obskuria | 2007 | 79:30 | Rock | World In Sound | CD | 11 |
| Obskuria | Burning Sea Of Green | 2010 | 45:48 | Rock | World In Sound | CD | 9 |
| Octopus Syng | Beyond The Karmadelic Coldness, There's The Lovedelic Warmth | 2004 | 41:00 | Rock | Band | CD | 11 |
| Octopus Syng | Birds Of Morning Are Never Late | 2007 | 45:37 | Rock | Nasoni Records | CD | 11 |
| ODA | ODA | 1972 | 43:33 | Rock | Hallucinations CDs | CD | 12 |
| Odyssey | Setting Forth | 1969 | 41:00 | Rock | Lion Productions | CD | 10 |
| Odyssey | Abysmal Despair | 2012 | 39:45 | Rock | Transubstans Records | CD | 8 |
| Ofege | Try And Love | 1973 | 32:25 | World | Academy LPs | CD | 8 |
| Ogre | Dawn Of The Proto-Man | 2003 | 49:16 | Rock | Wurmwhole Records | CD | 7 |
| Ogre | Seven Hells | 2006 | 56:24 | Metal | Leaf Hound Records | CD | 7 |
| Ogre | Plague Of The Planet | 2009 | 37:15 | Rock | Shadow Kingdom Records | CD | 1 |
| Ohio Players | Pleasure | 1972 | 31:10 | Funk | Westbound Records | CD | 9 |
| Oho | Okinawa | 1974 | 73:37 | Rock | Rockadrome | CD | 30 |
| OJM | Heavy | 2002 | 38:24 | Rock | Beard Of Stars Records | CD | 9 |
| OJM | The Light Album | 2004 | 35:53 | Rock | Go Down Records | CD | 9 |
| OJM | Under The Thunder | 2006 | 49:23 | Rock | Go Down Records | CD | 11 |
| OJM | Volcano | 2010 | 35:44 | Rock | Go Down Records | CD | 10 |
| Okta Logue | Ballads Of A Burden | 2010 | 41:01 | Rock | Nasoni Records | CD | 6 |
| Ola Balogun And Remi Kabaka | Black Goddess | 2011 | 00:00 | World | Soundway Records | LP | 6 |
| Olde Growth | Olde Growth | 2011 | 46:03 | Rock | MeteorCity Records | CD | 7 |
| Olivelawn | Sophomore Jinx! | 1992 | 34:23 | Rock | Headhunter Records | CD | 13 |
| Om | Variations On A Theme | 2004 | 45:08 | Metal | Holy Mountain | CD | 3 |
| Om | Conference Of The Birds | 2006 | 33:23 | Rock | Holy Mountain | CD | 2 |
| Om | Pilgrimage | 2007 | 32:18 | Metal | Southern Lord | CD | 4 |
| Om | Conference Live | 2009 | 41:17 | Metal | Important Records | LP | 2 |
| Om | God Is Good | 2009 | 34:08 | Metal | Drag City | CD | 4 |
| Om | Advaitic Songs | 2012 | 43:45 | Metal | Drag City | CD | 5 |
| Om (Catalonia) | Om | 1971 | 46:19 | Jazz | Picap | CD | 6 |
| Om Trio | Global Positioning Record | 2005 | 51:52 | Jazz | Black Beauty Records | CD | 14 |
| Om/Current 93 | Inerrant Rays Of Infallible Sun (Blackship Shrinebuilder) | 2006 | 16:22 | Rock | Durtro Jnana | CD | 2 |
| Omar Rodriguez Lopez Quintet | The Apocalypse Inside Of An Orange | 2008 | 60:59 | Rock | Infrasonic Sound | CD | 8 |
| Omnia Opera | Omnia Opera/Red Shift | 2012 | 148:24 | Rock | Esoteric Recordings | CD | 19 |
| Omnibus | Omnibus | 1970 | 40:37 | Rock | Mandala | CD | 12 |
| On A Pale Horse | On A Pale Horse | 2005 | 43:43 | Rock | Mushroom Cloud Records | CD | 11 |
| On Trial | Head Entrance | 1997 | 50:10 | Rock | SPV | CD | 7 |
| On Trial | New Day Rising | 1999 | 46:25 | Rock | Delerium | CD | 10 |
| On Trial | Blinded By The Sun | 2003 | 47:07 | Rock | Tee Pee Records | CD | 12 |
| On Trial | Head | 2003 | 47:48 | Rock | Molten Records | CD | 11 |
| On Trial | Live | 2004 | 49:38 | Rock | Molten Records | CD | 12 |
| On Trial | Forever | 2006 | 41:25 | Rock | Bad Afro Records | CD | 11 |
| One St. Stephen | One St. Stephen | 1975 | 33:54 | Rock | Radioactive Records | CD | 9 |
| Oneida | Anthem Of The Moon | 2001 | 47:26 | Rock | Jagjaguwar | CD | 12 |
| Oneida | Each One Teach One | 2002 | 58:10 | Rock | Jagjaguwar | CD | 9 |
| Oneida | Secret Wars | 2004 | 40:22 | Rock | Rough Trade Records | CD | 8 |
| Oneida | The Wedding | 2005 | 45:25 | Rock | Rough Trade Records | CD | 13 |
| Oneida | Happy New Year | 2006 | 44:07 | Rock | Jagjaguwar | CD | 11 |
| Oneida | Preteen Weaponry | 2008 | 39:22 | Rock | Jagjaguwar | CD | 3 |
| Oneida | Rated O | 2009 | 113:10 | Rock | Jagjaguwar | CD | 15 |
| Oneida | Absolute II | 2011 | 40:15 | Rock | Jagjaguwar | CD | 4 |
| Oneida | A List Of The Burning Mountains | 2012 | 38:06 | Rock | Jagjaguwar | LP | 2 |
| Oneida/Mugstar | Collisions 02 | 2011 | 32:11 | Rock | Rocket Recordings | LP | 2 |
| Opa | Back Home Lost 1975 Sessions | 2003 | 35:19 | Rock | Vampisoul | CD | 9 |
| The Open Mind | The Open Mind | 1969 | 52:34 | Rock | Sunbeam Records | CD | 16 |
| Operator Generator | Polar Fleet | 2001 | 32:13 | Rock | Man's Ruin Records | CD | 8 |
| Ophiucus | Ophiucus | 1972 | 64:06 | Rock | Lion Productions | CD | 20 |
| Orange Goblin | Frequencies From Planet Ten | 1997 | 47:21 | Rock | Rise Above Records | CD | 9 |
| Orange Goblin | Time Travelling Blues | 1998 | 71:00 | Rock | Rise Above Records | CD | 9 |
| Orange Goblin | The Big Black | 2000 | 48:14 | Rock | The Music Cartel | CD | 10 |
| Orange Goblin | Coup De Grace | 2002 | 53:41 | Rock | The Music Cartel | CD | 13 |
| Orange Goblin | Thieving From The House Of God | 2004 | 47:11 | Rock | Rise Above Records | CD | 11 |
| Orange Sunshine | Homo Erectus | 1969 | 40:01 | Rock | Headspin Records | CD | 8 |
| Orange Sunshine | Orange Sunshine | 2004 | 40:07 | Rock | Motorwolf Records | CD | 8 |
| Orange Sunshine | Bullseye Of Being | 2007 | 37:56 | Rock | Leaf Hound Records | CD | 5 |
| Orang-utan | Orang-utan | 1971 | 38:11 | Rock | Dr. Prog Records | LP | 8 |
| Orang-utan | Orang-Utan | 1971 | 38:44 | Rock | Lizard Records | CD | 8 |
| Orbital | Orbital | 1991 | 77:49 | Electronica | FFRR | CD | 11 |
| Orchestre Poly Rythmo De Cotonou | Echoes Hypnotiques | 2009 | 79:40 | Funk | Analog Africa | CD | 14 |
| Orchestre Poly-Rythmo | The 1st Album | 1973 | 33:13 | World | Analog Africa | CD | 4 |
| Orcus Chylde | Orcus Chylde | 2012 | 48:36 | Rock | World In Sound | CD | 8 |
| Organisation | Tone Float | 1970 | 41:14 | Rock | CD | 5 | |
| Orgone | The Killion Floor | 2007 | 76:02 | Funk | Ubiquity Recordings | CD | 17 |
| Orgone | Cali Fever | 2010 | 54:59 | Funk | Ubiquity Recordings | CD | 12 |
| Orient Express, The | The Orient Express | 1969 | 35:02 | Rock | Fallout | CD | 11 |
| Orion Express | The Orion Express | 1975 | 42:17 | Rock | Radioactive Records | CD | 13 |
| Orkustra, The | Adventures In Experimental Electric Orchestra From The San Francisco Psychedelic Underground | 2009 | 82:36 | Rock | Mexican Summer | LP | 11 |
| Orlando Julius And The Afro Sounders | Orlando Julius And The Afro Sounders | 1973 | 34:14 | World | Voodoo Funk | CD | 6 |
| Orne | The Tree Of Life | 2011 | 49:48 | Metal | Black Widow Records | CD | 7 |
| Orphan Egg | Orphan Egg | 1968 | 35:12 | Rock | Radioactive Records | CD | 12 |
| Orquesta Del Desierto | Orquesta Del Desierto | 2002 | 41:02 | Rock | MeteorCity Records | CD | 10 |
| Orquesta Del Desierto | Dos | 2004 | 37:36 | Rock | MeteorCity Records | CD | 10 |
| Os Mundi | 43 Minuten | 1972 | 44:40 | Rock | Brain Records | CD | 9 |
| Os Mutantes | Os Mutantes | 1968 | 35:58 | Rock | Lilith Records | CD | 11 |
| Osibisa | Osibisa | 1971 | 41:00 | Rock | AIM | CD | 7 |
| Osibisa | Sunshine Day - The Pye/Bronze Anthology | 1999 | 151:56 | Funk | Castle Music | CD | 31 |
| Osibisa | Osibisa/Woyaya | 2004 | 81:55 | Rock | Beat Goes On Records | CD | 14 |
| Osmosis | Osmosis | 1970 | 41:56 | Rock | Synton Archive Productions | CD | 12 |
| The Other Half | The Other Half | 1968 | 28:53 | Rock | Radioactive Records | CD | 10 |
| Otis Optic & The Option People | Otis Optic & The Option People | 2008 | 40:20 | Rock | Nasoni Records | CD | 12 |
| Otis Waygood Blues Band | Simply Otis Waygood | 1971 | 61:04 | Rock | Fresh Music | CD | 14 |
| Otis Waygood Blues Band | Otis Waygood Blues Band | 2000 | 46:24 | Rock | Fresh Music | CD | 12 |
| Out Of Focus | Wake Up | 1970 | 48:02 | Rock | Kuckuck Schallplatten | CD | 6 |
| Out Of Focus | Four Letter Monday Afternoon | 1972 | 94:35 | Rock | Kuckuck Schallplatten | CD | 8 |
| Out Of Focus | Palermo 1972 | 1972 | 76:03 | Rock | Garden Of Delights | CD | 6 |
| Out Of Focus | Rat Roads | 1972 | 50:51 | Rock | Garden Of Delights | CD | 9 |
| Out Of Order | Overload | 1998 | 21:45 | Rock | Boundless Records | CD | 4 |
| Outrage | 24-7 | 2002 | 65:34 | Metal | 30 Min. Records | CD | 14 |
| Outrageous Cherry | Universal Malcontents | 2009 | 36:21 | Rock | Alive Natural Sound Records | CD | 10 |
| The Outsiders | CQ | 1968 | 59:46 | Rock | RPM Records | CD | 19 |
| Ozric Tentacles | Pungent Effulgent | 1998 | 75:02 | Rock | Snapper Music | CD | 10 |