| MAME Name | Description | Official | Alternate | VC WS | ||
 | offroad | Ironman Ivan Stewart's Super Off-Road (rev 4) | 680 kB 06-Aug-2022 Download | - | 272 kB 06-Aug-2022 Download | |
 | offroadc | Off Road Challenge (v1.63) | - | - | 1.10 MB 06-Aug-2022 Download | |
 | offroadt | Ironman Ivan Stewart's Super Off-Road Track-Pak (rev 4?) | - | - | 285 kB 06-Aug-2022 Download | |
 | offtwall | Off the Wall (2/3-player upright) | 2.81 MB 06-Aug-2022 Download | - | 316 kB 06-Aug-2022 Download | |
 | ohmygod | Oh My God! (Japan) | - | - | 169 kB 06-Aug-2022 Download | |
| oisipuzl | Oishii Puzzle Ha Irimasenka | - | - | 198 kB 06-Aug-2022 Download | |
| okhota | Okhota | - | 7.94 MB 17-Sep-2023 Download | - | |
| olibochu | Oli-Boo-Chu (USA) | - | - | 149 kB 06-Aug-2022 Download | |
 | omegaf | Omega Fighter | - | - | 248 kB 06-Aug-2022 Download | |
 | omegrace | Omega Race (set 1) | 13.4 MB 06-Aug-2022 Download | - | 1.03 MB 06-Aug-2022 Download | |
 | one4all | One For All (0101503V, New Zealand) | - | 625 kB 06-Aug-2022 Download | - | |
 | oneshot | One Shot One Kill | - | - | 248 kB 06-Aug-2022 Download | |
| onna34ro | Onna Sanshirou - Typhoon Gal (rev 1) | - | - | 58.2 kB 06-Aug-2022 Download | |
| opaopa | Opa Opa (MC-8123, 317-0042) | - | - | 194 kB 06-Aug-2022 Download | |
 | openice | 2 On 2 Open Ice Challenge (rev 1.21) | - | - | 1.50 MB 06-Aug-2022 Download | |
 | opwolf | Operation Wolf (World, rev 2, set 1) | 3.50 MB 06-Aug-2022 Download | - | 5.56 MB 06-Aug-2022 Download | |
 | opwolf3 | Operation Wolf 3 (World) | 291 kB 06-Aug-2022 Download | - | 311 kB 06-Aug-2022 Download | |
 | orbit | Orbit | 529 kB 06-Aug-2022 Download | - | 209 kB 06-Aug-2022 Download | |
| orbitron | Orbitron | - | - | 485 kB 06-Aug-2022 Download | |
| orbs | Orbs (10/7/94 prototype?) | - | - | 238 kB 06-Aug-2022 Download | |
 | orchidms | Orchid Mist (0200849V, NSW/ACT) | - | 630 kB 06-Aug-2022 Download | - | |
 | orchidmsnz | Orchid Mist (0101241V, New Zealand) | - | 629 kB 06-Aug-2022 Download | - | |
 | ordyne | Ordyne (World) | - | - | 657 kB 06-Aug-2022 Download | |
| orlegend | Oriental Legend / Xiyou Shi E Zhuan (ver. 126) | - | - | 159 kB 06-Aug-2022 Download | |
 | orunners | OutRunners (World) | - | - | 955 kB 06-Aug-2022 Download | |
 | osbexec | Executive | 11.8 MB 06-Aug-2022 Download | - | - | |
 | osborne1 | Osborne-1 | 4.07 MB 06-Aug-2022 Download | - | - | |
| oscar | Psycho-Nics Oscar (World revision 0) | - | - | 188 kB 06-Aug-2022 Download | |
 | oscara5 | Oscar (0200348V, NSW/ACT) | - | 629 kB 06-Aug-2022 Download | - | |
 | osman | Osman (World) | 1.74 MB 06-Aug-2022 Download | - | 4.01 MB 06-Aug-2022 Download | |
| othldrby | Othello Derby (Japan) | - | - | 223 kB 06-Aug-2022 Download | |
 | othunder | Operation Thunderbolt (World, rev 1) | 263 kB 06-Aug-2022 Download | - | 66.9 kB 06-Aug-2022 Download | |
 | otwalls | Off the Wall (Sente) (10/16/84) | 178 kB 06-Aug-2022 Download | - | - | |
 | outfxies | The Outfoxies (World, OU2) | 1.79 MB 06-Aug-2022 Download | - | 195 kB 06-Aug-2022 Download | |
 | outrun | Out Run (sitdown/upright, Rev B) | 20.1 MB 06-Aug-2022 Download | - | 427 kB 06-Aug-2022 Download | |
 | outzone | Out Zone | 25.1 MB 06-Aug-2022 Download | - | 1.85 MB 06-Aug-2022 Download | |
 | overtop | Over Top | - | - | 2.30 MB 06-Aug-2022 Download | |
 | oz750 | Wizard OZ-750 | 1.21 MB 06-Aug-2022 Download | - | - | |
 | ozmawars | Ozma Wars (set 1) | - | - | 256 kB 06-Aug-2022 Download | |
| ozon1 | Ozon I | - | - | 423 kB 06-Aug-2022 Download | |
