| Obliterate | 2006 | ps2 |
| Ocean Commander | 2007 | ps2 |
| Ocean Commander | 2009 | wii |
| The Ocean Hunter | 1998 | arcade |
| Oddworld: Stranger's Wrath | 2020 | switch |
| Offensive | 1981 | arcade |
| Omega Assault | 2003 | ps1 |
| Omega Blast | 2018 | genesis |
| Omega Fighter | 1989 | arcade |
| Omega Fighter Special | 1989 | arcade |
| Omega Race | 1981 | arcade |
| Omikron - The Nomad Soul | 2000 | dreamcast |
| Omni | | arcade |
| On Duty | 2019 | lynx |
| One Shot One Kill | 1996 | arcade |
| Onslaught | 2009 | wii |
| Operacion Defender | 1981 | arcade |
| Operation - Vietnam | 2004 | nds |
| Operation Bear | 1987 | arcade |
| Operation C | 1991 | gb |
| Operation Flashpoint - Dragon Rising | 2009 | ps3, xbox360 |
| Operation Flashpoint - Dragon Rising | 2014 | ps3 |
| Operation Flashpoint - Elite | 2005 | xbox |
| Operation Flashpoint - Red River | 2011 | ps3, xbox360 |
| Operation Logic Bomb - The Ultimate Search & Destroy | 1993 | snes |
| Operation Thunder Hurricane | 1997 | arcade |
| Operation Thunderbolt | 1988 | arcade |
| Operation Tiger | 1998 | arcade |
| Operation Tiger Second Mission | 1998 | arcade |
| Operation Wolf | 1989 | nes, pcengine, sms |
| Operation Wolf | 2008 | wii |
| Operation Wolf | 1987 | arcade |
| Operation Wolf 3 | 1994 | arcade |
| The Operative - No One Lives Forever | 2002 | ps2 |
| The Orange Box | 2007 | ps3, xbox360 |
| Oratorio | 2022 | nes |
| Orbit | 2015 | xboxone |
| Orbit | 1978 | arcade |
| Orbite | 1979 | arcade |
| Orbitron | 1982 | arcade |
| The Order: 1886 | 2015 | ps4 |
| Ordyne | 2007 | wii |
| Oretachi Geesen Zoku - Contra | 2006 | ps2 |
| Oretachi Geesen Zoku - Moon Cresta | 2005 | ps2 |
| Oretachi Geesen Zoku - Pooyan | 2006 | ps2 |
| Oretachi Geesen Zoku - Scramble | 2005 | ps2 |
| Oretachi Geesen Zoku - Sonic Wings | 2005 | ps2 |
| Oretachi Geesen Zoku - Terra Cresta | 2005 | ps2 |
| Oretachi Geesen Zoku - Thunder Cross | 2007 | ps2 |
| Oretachi Geesen Zoku - Time Pilot | 2005 | ps2 |
| Oretachi no Sabage Portable | 2008 | psp |
| Oretachi no Sabage Versus | 2010 | psp |
| Orguss | 1984 | sg1000 |
| Orius | 1991 | arcade |
| Otocky | 1987 | fds |
| Otomedius | 2007 | arcade |
| Otomedius Excellent | 2011 | xbox360 |
| Otomedius Gorgeous! | 2008 | xbox360 |
| Otxo | 2024 | switch |
| Out Live - Be Eliminate Yesterday | 1997 | ps1 |
| Out Zone | 1990 | arcade |
| Out of This World + Helicopter Rescue | 1979 | o2 |
| OutTrigger | 1999 | arcade, dreamcast |
| Outlaw | 1976 | arcade |
| Outriders | 2021 | ps4, xboxone |
| Over Drive | 1990 | arcade |
| Over Horizon | 1991 | nes |
| Over Horizon - Fei Li Hangdao | 1991 | nes |
| Overboard! | 1997 | ps1 |
| Overdriven Reloaded: Special Edition | 2018 | xboxone |
| Overkill & Lunar-C | 1994 | cd32 |
| Overkill's The Walking Dead | 2018 | xboxone |
| Overload | 2018 | ps4, xboxone |
| Override | 1991 | pcengine |
| Overwatch | 2016 | ps4, switch, xboxone |
| Overwatch 2 | 2023 | ps4, switch, xboxone |
| Ozma Wars | 1979 | arcade |
| Ozon I | 1983 | arcade |
| P'Radikus Conflict | 1990 | nes |
| P's Attack | 2004 | arcade |
| P-47 Aces | 1995 | arcade |
| P-47 II MD | 2025 | genesis |
| P-47: The Freedom Fighter | 1988 | arcade, pcengine |
| P-52 Sea Battle | 1992 | svision |
| P.N. 03 | 2003 | gc |
| PC Denjin - Punkic Cyborgs | 1992 | pcengine |
| PC Denjin - Punkic Cyborgs | | wii |
| PC Engine Best Collection - Soldier Collection | 2008 | psp |
| PO'ed | 1995 | 3do, ps1 |
| PO'ed: Definitive Edition | 2024 | ps4 |
| Pacom Invader | 1979 | arcade |
| Painkiller - Hell & Damnation | 2013 | ps3, xbox360 |
| Painkiller - Hell Wars | 2006 | xbox |
| Pajaro del Espacio | 1980 | arcade |
| Paladin | 2017 | xboxone |
| Paladins | 2018 | switch, xboxone |
| Pang | 1989 | arcade |
| Pang! 3 | 1995 | arcade |
| Pang! 3: Kaitou Tachi no Karei na Gogo | 1995 | arcade |
| Panorama Cotton | 1994 | genesis, ps4, switch |