| # | Company name | Role | # of projects |
|---|---|---|---|
| 1 | OCI Associates, Inc. | MEP engineering | 26 |
| 2 | OCI Associates, Inc. | MEP engineering | 1 |
| 3 | Oliver D. Billing & Associates | MEP engineering | 2 |
| 4 | Omega Engineering L.L.C. | MEP engineering | 1 |
| 5 | One Zone Asia (Philippines) Inc. | MEP engineering | 1 |
| 6 | Optima Power & Energy Solutions, LLC | MEP engineering | 1 |
| 7 | Optimal Engineering spol. s.r.o. | MEP engineering | 1 |