| # | Company name | Role | # of projects |
|---|---|---|---|
| 1 | O & Associates Inc | Consultancy | 0 |
| 2 | O & Associates Inc | Consultancy | 1 |
| 3 | O & Gere Engineers | Consultancy | 5 |
| 4 | O & Schoenlank | Consultancy | 0 |
| 5 | O Construction | Consultancy | 1 |
| 6 | O Inc. | Consultancy | 0 |
| 7 | O M B Electrical Engineers | Consultancy | 0 |
| 8 | O'Donnell Consulting Engineers, Inc. | Consultancy | 0 |
| 9 | Oates Associates Consulting Engineers | Consultancy | 0 |
| 10 | OBH-Gruppen A/S | Consultancy | 1 |
| 11 | Oca Global | Consultancy | 1 |
| 12 | OCB Reprographics | Consultancy | 4 |
| 13 | OCB Reprographics | Consultancy | 15 |
| 14 | OEC Consulting | Consultancy | 8 |
| 15 | Oest&Partner | Consultancy | 3 |
| 16 | OGCB | Consultancy | 5 |
| 17 | Ohio Blue Print Company, Inc. | Consultancy | 2 |
| 18 | Oliveri Printing Corp. | Consultancy | 1 |
| 19 | OLM Consultancy | Consultancy | 2 |
| 20 | Olsen-Peterson Engineers Inc | Consultancy | 1 |