| 29600 | Odd One Out | ZX81 16K | English |
| 34542 | Odyssey | ZX81 16K | English |
| 40712 | Ohm's Law | ZX81 16K | English |
| 41022 | Oilrig | ZX81 16K | English |
| 29602 | Old Forty-Niner | ZX81 16K | English |
| 29142 | Olympiade | ZX81 16K | Dutch |
| 43853 | Olympiade | ZX81 16K | German |
| 29603 | Olympics | ZX81 16K | English |
| 43520 | Omega Phoenix | ZX81 16K | English |
| 41148 | On Final | ZX81 16K | English |
| 41607 | On X Goto/Gosub | ZX81 16K | English |
| 31956 | One Little Ghost | ZX81 16K | English |
| 33436 | One Little Ghost - Chroma Edition | ZX81 16K | - |
| 40884 | One-Armed Bandit | ZX81 16K | English |
| 41629 | Oodunnit? | ZX81 16K | English |
| 28992 | Op Avontuur Met De Enterprise | ZX81 16K | Dutch |
| 37417 | Opération Panther | ZX81 16K | French |
| 29145 | Orbiter | ZX81 16K | Dutch |
| 43697 | Ordidactic | ZX81 16K | French |
| 29180 | Oregon Trail | ZX81 16K | English |