| Operation Gunship (1989) | 5,000 | 23 |
| Operation Hardcore (2016) | 7,525 | 36 |
| Operation Harrier (1990) | 3,094 | 18 |
| Operation Logic Bomb (1993) | 258,734 | 291 |
| Operation Lovecraft: Fallen Doll (2022) | 984,821 | 82 |
| Operation Marakudja (2024) | 87 | 6 |
| Operation Market Garden (1985) | 2,251,642 | 149 |
| Operation Neptune (1991) | 200,916 | 176 |
| Operation Octo (2025) | 64,563 | 39 |
| Operation Pig (2018) | 624,138 | 25 |
| Operation Red Dragon (2017) | 414 | 5 |
| Operation Sabotage (1982) | 9,923 | 7 |
| Operation Secret Storm (1991) | 111,886 | 55 |
| Operation Shadow (2004) | 163,489 | 69 |
| Operation Space Force (2024) | 26 | 7 |
| Operation Spacehog (2000) | 2,681 | 6 |
| Operation Stealth (1990) | 837,622 | 219 |
| Operation STEEL (2022) | 52,532 | 83 |
| Operation Thunderbolt (1988) | 660,883 | 404 |
| OPERATION TIGER (1998) | 17,621 | 11 |
| Operation Valor (2023) | 74,101 | 101 |
| Operation Warcade VR (2017) | 612,622 | 110 |
| Operation Wolf (1987) | 3,198,561 | 1,467 |
| Operation Wolf 3 (1994) | 140,031 | 109 |
| Operation Wolfsburg (2010) | 68,701 | 41 |
| Operation WOW (2011) | 4,324 | 14 |
| Operation7 (2008) | 18,501,486 | 3,931 |
| Operation7: Showdown (2020) | 172,673 | 237 |
| Operation: Cleanstreets (1988) | 24,228 | 32 |
| Operation: Desert Storm (1991) | 341,168 | 112 |
| Operation: Eco-Nightmare (1997) | 8,938 | 18 |
| Operation: Harsh Doorstop (2023) | 33,485,776 | 3,474 |
| Operation: Inner Space (1994) | 33,185 | 22 |
| Operation: Matriarchy (2005) | 102,356 | 148 |
| Operation: Pinkeye (2022) | 1,610 | 21 |
| Operation: Polarity Hook (2019) | 80 | 3 |
| Operation: Polygon Storm (2024) | 160,131 | 128 |
| Operation: Tango (2020) | 29,481,228 | 6,720 |
| Operation: VICUS (2022) | 19 | 1 |
| Operation: Vietnam (2007) | 82,943 | 23 |
| Operation: Weather Disaster (1995) | 51,633 | 14 |
| The Operational Art of War III (2006) | 37,099 | 65 |
| The Operative: No One Lives Forever (2000) | 4,179,636 | 1,555 |
| The Operator (2024) | 124,000,229 | 17,429 |
| Operator 41 (2019) | 6,687 | 30 |
| Operator Ace's Simple Infinite Survival (2024) | 19 | 2 |
| Operator8 (2022) | 6,200 | 45 |
| Operator: Observation (2026) | 0 | 0 |
| Operencia: The Stolen Sun (2019) | 2,702,305 | 2,713 |
| OPG: Clan Wars (2024) | 1,294 | 7 |
| Ophidian Wars: Opac's Journey (2010) | 416 | 4 |
| Opoona (2007) | 626,931 | 693 |
| OPPAI Ero App Academy Bigger, Better, Electric Boobaloo! (2023) | 118,185 | 3 |
| OPPAI Succubus Academy Sucky and Busty, Demonic and Lusty! (2024) | 117,852 | 2 |
| Oppaidius Desert Island! (2021) | 6,529 | 1 |
| Oppaidius Summer Trouble! (2018) | 17,574 | 3 |
| Optika (2016) | 92,778 | 14 |
| Opus Castle (2021) | 745,248 | 1,910 |
| Opus Magnum (2017) | 3,108,206 | 2,242 |
| Opus: Echo of Starsong (2021) | 1,854,085 | 2,337 |
| Opus: Rocket of Whispers (2017) | 618,680 | 937 |
| Opus: The Day We Found Earth (2015) | 810,203 | 591 |
| Oracle of Forgotten Testament (2018) | 10,817 | 41 |
| Oracle Trials (2021) | 10,074 | 22 |
| The Oracle's Cave (1984) | 36,322 | 27 |
| Orake (2016) | 20,801 | 11 |
| The Orange Box (2007) | 12,104,874 | 1,081 |
| Orange Cast: Sci-Fi Space Action Game (2021) | 231,651 | 125 |
| Orange Moon (2017) | 30,092 | 47 |
| Orange Santa (2021) | 0 | 0 |
| Orangeblood (2020) | 393,792 | 420 |
| Orb and the Stars (2021) | 68 | 1 |
| Orb of Aeternum (2024) | 4,401 | 5 |
| Orb of Creation (2022) | 619,238 | 367 |
| Orb Of The Watcher (2024) | 164 | 7 |
