| O T Electric INC | Opetio Okusi | — | (510) 906 7062 | Electricians | Oakland · Alameda County | — | — |
| O Valley Construction | Enrique Orlando Valle Sobalvarro | — | (510) 677 5803 | GC, remodel, ADU | San Leandro · Alameda County | — | — |
| O'callaghan Construction | Collin Michael O'callaghan | — | (925) 548 2601 | GC, remodel, ADU | Pleasanton · Alameda County | — | — |
| O'clavin Painting | Patrick Derek Clavin | — | (510) 867 7873 | Windows, patio, painters | Alameda · Alameda County | — | — |
| O'connell Constructs LLC | Sean Patrick O'connell | — | (419) 348 8361 | GC, remodel, ADU | Emeryville · Alameda County | — | — |
| O'frankie Construction Corporation | Olivia Ming Lum | — | (415) 678 8318 | GC, remodel, ADU | Alameda · Alameda County | — | — |
| O'leary Construction | Christopher Ian O'leary | — | (510) 517 0269 | GC, remodel, ADU | Berkeley · Alameda County | — | — |
| O'neill Built Construction | Patrick James O'neill | — | (510) 394 4614 | GC, remodel, ADU | Alameda · Alameda County | — | — |
| Oak Bay Builder | Oak Bay Builder | — | (510) 847 3924 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| Oak General Construction INC | Zugaide Samuel Bautista | — | (510) 542 3483 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| Oak Iron Construction LLC | Hu Li | info@oakironconstruction.com | (669) 500 2535 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| Oak Leaf Painting And Maintenance INC | Adam Jon Shahoian | — | (510) 473 7140 | Windows, patio, painters | Oakland · Alameda County | — | — |
| Oak Park Construction | Henry Anthony Carvajal | — | (925) 939 4080 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| Oak Patch Building | Oak Patch Building | — | (510) 599 5933 | GC, remodel, ADU | Alameda · Alameda County | — | — |
| Oakal Construction INC | Rafael Toscano-Birrueta | — | (510) 849 7506 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| Oakland Aesthetics Tree Care | Oakland Aesthetics Tree Care | — | (510) 593 9747 | Tree | Berkeley · Alameda County | — | — |
| Oakland Construction | Guillermo Ramirez Rodriguez | — | (510) 355 5566 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| Oakland Ecostar Roofing Group | Oakland Ecostar Roofing Group | info@ecostaroofingroup.com | (866) 402-6821 | Other roofers | Oakland · Alameda County | — | — |
| Oakland Rooter & Plumbing | Oakland Rooter & Plumbing | — | (510) 479 1129 | Other | Oakland · Alameda County | — | — |
| Oakland Stone Landscaping Design | Oakland Stone Landscaping Design | — | (301) 741 5168 | Windows, patio, painters | Oakland · Alameda County | — | — |
| Oakland United Studios | Paul James De Clercq | — | (510) 633 5110 | Other | Oakland · Alameda County | — | — |
| Oakland Wood Floors | Oakland Wood Floors | — | (650) 906 9403 | Other | Oakland · Alameda County | — | — |
| Oakline Electric | Robert Perez | contact@oakline-electric.com | (510) 909 0478 | Electricians | Oakland · Alameda County | — | — |
| Oakline Electric LLC | Oswaldo Toscano | contact@oakline-electric.com | (510) 603 9687 | Electricians | Oakland · Alameda County | — | — |
| Oakstead | Geoffrey Philip Shuey | — | (510) 712 6373 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| Oakview Shutters And Blinds | Oakview Shutters And Blinds | — | (925) 634 9549 | Other | Oakland · Alameda County | — | — |
| Oates Roofing | Clinton Thomas Oates | — | (510) 750 5645 | Other roofers | Fremont · Alameda County | — | — |
| Obr Electric Limited Liability Co | Ramirez Oscar Barragan | — | (510) 566 8106 | Electricians | Oakland · Alameda County | — | — |
| Obra Construction & Building Services LLC | Garcia Pablo Vazquez | — | (510) 316 7128 | GC, remodel, ADU | Berkeley · Alameda County | — | — |
| Oc Jones & Sons Bridgeway Civil Constructors A Joint Venture | Civil Constructors INC Bridgeway | — | (510) 526 3424 | Other | Berkeley · Alameda County | — | — |
| Oc Plumbing & Water Heaters | Oc Plumbing & Water Heaters | — | (510) 648 7729 | Other | Newark · Alameda County | — | — |
| Ocd Plan & Build INC | Tamar Benshalom | — | (510) 910 2256 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| Ocean Bay Plumbing INC | Elisea Raul Paniagua | rmusante@oceanbayplumbing.com | (408) 892 2741 | Other | Hayward · Alameda County | — | — |
| Ocean Plumbing | Ocean Plumbing | — | (510) 829 5135 | Other | Oakland · Alameda County | — | — |
| Ocean Remodel INC | Yossef Shalom Sapir | contact@oceanremodel.com | (310) 744 5575 | GC, remodel, ADU | Castro Valley · Alameda County | — | — |
| Oculis LLC | Hector Luis Ibarra | — | (925) 404 9170 | GC, remodel, ADU | Pleasanton · Alameda County | — | — |
| Off The Street General Contracting INC | Ronald Eugene Germann | — | (510) 384 9801 | GC, remodel, ADU | Hayward · Alameda County | — | — |
| Og General Builders INC | Gonzalez Omar Gil | — | (510) 361 8882 | GC, remodel, ADU | Hayward · Alameda County | — | — |
| Ok Heating And Air Conditioning INC | Robert Jr Kathain | — | (925) 371 2665 | HVAC | Livermore · Alameda County | — | — |
| Oki Landscaping INC | David Vanegas | — | (562) 219 1270 | Windows, patio, painters | Oakland · Alameda County | — | — |