| # | Company name | Role | # of projects |
|---|---|---|---|
| 1 | O & Naccarato Inc. | Structural engineering | 2 |
| 2 | O Naccarato Mignogna & Jackson Inc | Structural engineering | 0 |
| 3 | O Pavlo & Associates | Structural engineering | 0 |
| 4 | O.E. Olsen & Associates, Inc. | Structural engineering | 24 |
| 5 | O'Connor Freeman & Associates | Structural engineering | 1 |
| 6 | O'Connor Sutton Cronin | Structural engineering | 18 |
| 7 | O'Donnell & Naccarato, Inc. | Structural engineering | 32 |
| 8 | O'Donnell, Naccarato & Macintosh | Structural engineering | 1 |
| 9 | O'Donnell, Naccarato, Mignogna & Jackson, Inc. | Structural engineering | 45 |
| 10 | O'Kon & Company, Inc. | Structural engineering | 1 |
| 11 | Oak Engineering | Structural engineering | 3 |
| 12 | Oakley & Oakley | Structural engineering | 1 |
| 13 | Oakley & Oakley Architecture/engineering | Structural engineering | 0 |
| 14 | Obler & Clarke | Structural engineering | 2 |
| 15 | Oboler & Clarke | Structural engineering | 7 |
| 16 | OC Engineering | Structural engineering | 3 |
| 17 | Ocmulgee Associates | Structural engineering | 0 |
| 18 | Odeh Engineers | Structural engineering | 7 |
| 19 | Oftedal, Locke, Broadsten & Associates, Inc. | Structural engineering | 1 |
| 20 | Okg Engineers Llc | Structural engineering | 1 |