| OIOcci INC. Wwtp | Fulton | MO | — | ◇ UNVERIFIED |
 Occupational Development Center INC Dba Custom Pro | Bemidji | MN | — | ◇ UNVERIFIED |
| OSOcean Steel Corporation | Binghamton | NY | — | ◇ UNVERIFIED |
| OBOeg Building Materials INC. | Matawan | NJ | — | ◇ UNVERIFIED |
| OFOem Fabricators INC | Neillsville | WI | — | ◇ UNVERIFIED |
| OSOesterlings Sandblasting/butler | Butler | PA | — | ◇ UNVERIFIED |
| OAOgden Art Metal INC. | Murray | UT | — | ◇ UNVERIFIED |
| OOgletree's | Saint Helena | CA | — | ◇ UNVERIFIED |
| OCOglivie Company INC the | Astoria | OR | — | ◇ UNVERIFIED |
| OHO H I Company | Stockton | CA | — | ◇ UNVERIFIED |
| OCOhi Company | Stockton | CA | — | ◇ UNVERIFIED |
| OSOhio Steel Industries (0145000318) | Pataskala | OH | — | ◇ UNVERIFIED |
| OSOhio Steel Industries, INC. | Summit Station | OH | — | ◇ UNVERIFIED |
| OVOhio Valley Fabrication and Energy INC. | Wheeling | WV | — | ◇ UNVERIFIED |
| OIOiw, INC. | Pelham | AL | — | ◇ UNVERIFIED |
| OLOiw LLC | Oakdale | PA | — | ◇ UNVERIFIED |
| OKO & K American CORP. | Chicago | IL | — | ◇ UNVERIFIED |
| OBOld Bridge Metal Fabrication Inc. | Riverside | CA | — | ◇ UNVERIFIED |
| OIOldcastle Infrastructure - Azusa 10th | Azusa | CA | — | ◇ UNVERIFIED |
| OIOldcastle Infrastructure - Azusa Dalou | Azusa | CA | — | ◇ UNVERIFIED |
| OCOlson & Company Steel | Fresno | CA | — | ◇ UNVERIFIED |
| OSOlson Steel | San Leandro | CA | — | ◇ UNVERIFIED |
| OTOlympus Technologies Incorporated | Eugene | OR | — | ◇ UNVERIFIED |
| ONOmega Natchiq New Iberia Facility | New Iberia | LA | — | ◇ UNVERIFIED |
| OSOmega Steel Products, INC | Jemison | AL | — | ◇ UNVERIFIED |
| OMO & M Fabricators, LLC | Pensacola | FL | — | ◇ UNVERIFIED |
| OIOmni Industrial Services | Buffalo | WV | — | ◇ UNVERIFIED |
| OSOne Source Systems LLC | Vicksburg | MS | — | ◇ UNVERIFIED |
| OTOn Time Fab INC | Saint Joseph | KY | — | ◇ UNVERIFIED |
| OFOpc Fabrication and Equipment, INC. (fn) | Phoenix | AZ | — | ◇ UNVERIFIED |
| OSOrange State Steel | Bartow | FL | — | ◇ UNVERIFIED |
| OSOrange State Steel Construction, INC | Pinellas Park | FL | — | ◇ UNVERIFIED |
| OSOrange State Steel Construction, INC. | Riverview | FL | — | ◇ UNVERIFIED |
| OCOrco Construction Supply | Bloomington | CA | — | ◇ UNVERIFIED |
| ODOreco Duct System INC | Baldwin Park | CA | — | ◇ UNVERIFIED |
| OIOregon Iron Works Hidden Way | Vancouver | WA | — | ◇ UNVERIFIED |
| OIOregon Iron Works INC 3001 | Vancouver | WA | — | ◇ UNVERIFIED |
| OPOregon Pacific Structural Fabrication, LLC | Mulino | OR | — | ◇ UNVERIFIED |
| OTOrganic Transit INC. | Durham | NC | — | ◇ UNVERIFIED |
| OMOrion Marine Construction, INC | Tampa | FL | — | ◇ UNVERIFIED |
| OIOrlando Iron Works | Paterson | NJ | — | ◇ UNVERIFIED |
| OMOrnamental Metalworks INC | Decatur | IL | — | ◇ UNVERIFIED |
| OWOsborne Welding, INC. | Hampton | VA | — | ◇ UNVERIFIED |
| OAOshkosh Aerotech - Jetway Systems | Ogden | UT | — | ◇ UNVERIFIED |
| OIOssi's Iron Works | Las Vegas | NV | — | ◇ UNVERIFIED |
| OSOutland Steel, INC. | Caldwell | ID | — | ◇ UNVERIFIED |
| OIOutlaw Industries, LLC | Clinton | LA | — | ◇ UNVERIFIED |
| OSOwens & Sons, INC. | Metairie | LA | — | ◇ UNVERIFIED |
| OBOzark Barge & Dock Service Inc.* | Gravois Mills | MO | — | ◇ UNVERIFIED |
| PIPacal Industries LLC | La Crosse | WI | — | ◇ UNVERIFIED |
