| Ong Leng Kak | 3660 | Electrical | 2001-09-18 | Ohmz and Associates |
| Ong Lian Huat | 3379 | Civil | 1998-03-17 | Demaco Consultants Pte. Ltd. |
| Ong Lip Hee | 5262 | Civil | 2019-10-17 | CPG Consultants Pte Ltd |
| Ong Meng Teck | 4595 | Electrical | 2014-05-15 | SP Group |
| Ong Meng Wan | 4111 | Civil | 2007-01-26 | Jacobs International Consultants Pte. Ltd. |
| Ong Min Sing | 4038 | Electrical | 2006-05-16 | SP Group |
| Ong Ngee Yong | 3523 | Mechanical | 2000-01-18 | Building Engineering and Management Systems |
| Ong Oon Chien | 2831 | Electrical | 1992-06-15 | Guthrie Engineering (S) Pte Ltd |
| Ong Pang Onn | 4453 | Mechanical | 2012-06-21 | K&J Engineering Pte Ltd |
| Ong Pin Yi @ Ong Yan Xiang | 5874 | Electrical | 2026-04-23 | CPG Consultants Pte Ltd |
| Ong Ser Huan | 0753 | Electrical | 1973-09-20 | Enkon International Consulting Engineers Pte Ltd |
| Ong Shu Xian Caroline | 5276 | Civil | 2019-10-17 | Beca Carter Hollings & Ferner (S.E.Asia) Pte Ltd |
| Ong Thiam Guan | 3673 | Mechanical | 2001-10-16 | OX+A Consultants |
| Ong Toon Lian | 4414 | Civil | 2011-10-20 | OTL Engineering & Safety Consultancy Pte. Ltd. |
| Ong Wee Kiat | 3748 | Civil | 2002-08-16 | Ang & Ong Consultants Pte. Ltd. |
| Ong Wei Ren Shunski | 5767 | Electrical | 2025-05-22 | Land Transport Authority |
| Ong Zhen Yun | 5425 | Civil | 2021-11-25 | Land Transport Authority |
| Ong Zongjue | 5534 | Mechanical | 2023-04-27 | Galmon (S) Pte Ltd |
| Ooi Poh Hai | 4607 | Civil | 2014-06-23 | A-Terra Consultants Pte. Ltd. |
| Ooi Sim Thung | 3711 | Civil | 2002-06-21 | KK Lim & Associates Pte. Ltd. |
| Ooi Wei Sheng | 5374 | Electrical | 2021-01-21 | RED Engineering Tractebel (Singapore) Pte. Ltd. |
| Ooi Wenyao | 5892 | Electrical | 2026-05-28 | SP PowerGrid Ltd |
| Oong Eng Choon | 5490 | Mechanical | 2022-11-24 | National University Of Singapore |
| Oskar Sigl | 3720 | Civil | 2002-06-21 | Geoconsult Asia Singapore Pte Ltd |
| Ow Chun Nam | 1879 | Civil | 1983-03-11 | - |
| Ow Peng Peng | 4267 | Civil | 2007-07-19 | PUB, Singapore's National Water Agency |
| Ow Yeong Kah Leong | 5733 | Civil | 2025-02-27 | Sembcorp Specialised Construction Pte Ltd |
| P Sivanandam | 3623 | Electrical | 2001-05-11 | SP PowerGrid Limited |
| Pam Chee How | 4948 | Electrical | 2017-10-23 | Euler Electrical Engineering Private Limited |
| Pan Yunru | 5589 | Electrical | 2023-10-26 | Land Transport Authority |