| ONTA LIMITED | Private company limited by shares | Dissolved |
| ONTACT LIMITED | Private company limited by shares | Live |
| Ontact Asia Limited | Private company limited by shares | Live |
| ONTACT PROTOCOL LIMITED | Private company limited by shares | Live |
| ONTAI LIMITED | Private company limited by shares | Dissolved |
| ONTAK LIMITED | Private company limited by shares | Dissolved |
| ONTAK LIMITED | Private company limited by shares | Live |
| ONTAK INVESTMENT LIMITED | Private company limited by shares | Dissolved |
| ONTAL COMPANY LIMITED | Private company limited by shares | Dissolved |
| ONTAL DESIGN LIMITED | Private company limited by shares | Dissolved |
| ONTALENT LIMITED | Private company limited by shares | Dissolved |
| Ontandra Limited | Private company limited by shares | Live |
| ONTANK INVESTMENTS AND FINANCE LIMITED | Private company limited by shares | Dissolved |
| ONTAR LIMITED | Private company limited by shares | Live |
| ONTARGET LIMITED | Private company limited by shares | Live |
| On-Target Advertising Limited | | Live |
| ONTARGET ASIA LIMITED | Private company limited by shares | Dissolved |
| ONTARIO LIMITED | Private company limited by shares | Dissolved |
| ONTARIO COMPANY LIMITED | | Live |
| NO. 505746 ONTARIO (HK) LIMITED | Private company limited by shares | Dissolved |
| Ontario eSchool Asia Limited | Private company limited by shares | Live |
| ONTARIO CENTURY ENTERPRISE LIMITED | Private company limited by shares | Dissolved |
| ONTARIO ENTERPRISES LIMITED | Private company limited by shares | Dissolved |
| ONTARIO FINANCE LIMITED | Private company limited by shares | Live |
| ONTARIO FINANCE AND INVESTMENT COMPANY, LIMITED | Private company limited by shares | Dissolved |
| ONTARIO INVESTMENT LIMITED | Private company limited by shares | Dissolved |
| LAKE ONTARIO LIMITED | Private company limited by shares | Live |
| PORT ONTARIO LIMITED | Private company limited by shares | Dissolved |
| Talent Ontario Limited | | Live |
| ONTARIO TECHNOLOGY LIMITED | Private company limited by shares | Dissolved |
| ONTARIO-CENTURY COMPANY LIMITED | Private company limited by shares | Dissolved |
| ONTARKEE COMPANY LIMITED | Private company limited by shares | Dissolved |
| ONTARY COMPANY LIMITED | Private company limited by shares | Dissolved |
| ONTASK LIMITED | Private company limited by shares | Live |
| ONTAT ASIA LIMITED | Private company limited by shares | Dissolved |
| ON.TA.U. Limited | Private company limited by shares | Live |