| 41148 | On Final | ZX81 16K | English |
| 25487 | On Moon! | ZX-Spectrum 48K | English |
| 15805 | On the Burgle! | ZX-Spectrum 48K | English |
| 39604 | On the Emperor's Secret Service | ZX-Spectrum 48K | English |
| 24071 | Ondas | ZX-Spectrum 48K | Spanish |
| 39779 | One Day Cricket | ZX-Spectrum 48K | English |
| 42665 | One Key Tapeworm | ZX-Spectrum 48K | English |
| 39402 | One Line Snake | ZX-Spectrum 16K | Multi-language: English, Spanish |
| 25599 | One Man and His Job | ZX-Spectrum 48K | English |
| 40884 | One-Armed Bandit | ZX81 16K | English |
| 41113 | One-Armed Bandit | ZX80 | English |
| 41629 | Oodunnit? | ZX81 16K | English |
| 28992 | Op Avontuur Met De Enterprise | ZX81 16K | Dutch |
| 34676 | Operation - Labyrinth Fall | ZX-Spectrum 48K/128K | English |
| 44715 | Operation Bee | ZX-Spectrum 16K | English |
| 10017 | Operation Gunshot | ZX-Spectrum 48K/128K | English |
| 44300 | Operation Moo | ZX-Spectrum 128K | English |
| 16724 | Operation Sirius | ZX-Spectrum 48K | German |
| 37417 | Opération Panther | ZX81 16K | French |
| 36688 | Orb Run | ZX-Spectrum Next | English |