| Nyap Fat Ming | 2224 | Electrical | 1986-02-03 | Action Engineer Services |
| Nyeow Low Yin | 5076 | Chemical | 2018-05-17 | SJD Consultants Pte. Ltd. |
| Oei Swan San | 4588 | Mechanical | 2014-03-20 | Bescon Engineering Services Pte. Ltd. |
| Oh Chun Siang | 5229 | Mechanical | 2019-06-20 | One Engineering (Mech) Pte. Ltd. |
| Oh Gui Yong | 4360 | Electrical | 2010-06-17 | Aster Chemicals and Energy Pte. Ltd. |
| Oh Hui Sung | 4657 | Electrical | 2014-10-21 | ON Engineers Pte. Ltd. |
| Oh Wee Siong | 5191 | Mechanical | 2018-12-14 | OHWS Engineers Pte. Ltd. |
| Ong Beng Koon Edwin | 3276 | Civil | 1996-10-02 | Surbana Jurong Consultants Pte. Ltd. |
| Ong Calvin | 5298 | Civil | 2020-01-16 | PUB, Singapore's National Water Agency |
| Ong Chee Wee | 4336 | Civil | 2009-11-19 | One Smart Engineering Pte. Ltd. |
| Ong Cher Shyan | 4863 | Mechanical | 2017-03-23 | RED Engineering Tractebel (Singapore) Pte Ltd |
| Ong Chia Wai | 4902 | Civil | 2017-07-18 | ECAS Consultants Pte. Ltd. |
| Ong Chin How | 3695 | Mechanical | 2002-03-19 | DNO Engineers Pte. Ltd. |
| Ong Chin Soon | 3499 | Electrical | 1999-08-17 | NA |
| Ong Chong Ping | 1583 | Mechanical | 1981-03-24 | Eletrain Pte. Ltd. |
| Ong Chong Yao | 4647 | Mechanical | 2014-10-21 | - |
| Ong Chuan Hock | 3336 | Civil | 1997-07-15 | - |
| Ong Chung Wei | 4826 | Mechanical | 2016-10-18 | - |
| Ong Eng Hwee | 3548 | Civil | 2000-05-16 | OEH Consultants |
| Ong Guan Thong | 5755 | Electrical | 2025-03-27 | Arup Singapore Private Limited |
| Ong Hai Tien | 4563 | Mechanical | 2013-10-17 | Tritont Consulting LLP |
| Ong Hong Sheng Ken | 5522 | Electrical | 2023-03-23 | SP Group |
| Ong Hun Kok Anthony | 3672 | Mechanical | 2001-10-16 | M.Moser Associates (S) Pte Ltd |
| Ong Kean Hoe | 3871 | Electrical | 2004-03-16 | HPX Consulting Engineers Pte. Ltd. |
| Ong Kian Hai | 4706 | Electrical | 2015-08-18 | Land Transport Authority |
| Ong Kim Sze | 2412 | Civil | 1988-08-17 | - |
| Ong Kok Cheng | 2735 | Electrical | 1991-11-20 | SMRT Trains Ltd. |
| Ong Kok Chye Benjamin | 2136 | Mechanical | 1985-04-16 | Infra-Asia Consultants |
| Ong Kuang Hao | 5622 | Electrical | 2024-03-28 | Energy Market Authority |
| Ong Lay Leng | 3783 | Civil | 2003-01-27 | GeoAlliance Consultants Pte. Ltd. |