| Olczak General Contractors INC | Zachary Coleman Olczak | — | (615) 495 2154 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| Older's Landscaping | Older's Landscaping | — | (408) 687 2496 | Windows, patio, painters | Pleasanton · Alameda County | — | — |
| Olga Garibay Plumbing | Olga Garibay Plumbing | — | (510) 228 7052 | Other | Castro Valley · Alameda County | — | — |
| Olivas Construction | Olivas Medina Marino | — | (510) 209 3718 | GC, remodel, ADU | Hayward · Alameda County | — | — |
| Olive Remodeling | Olive Remodeling | — | (510) 393 1577 | GC, remodel, ADU | Emeryville · Alameda County | — | — |
| Oliver & Son | Oliver & Son | — | (510) 579 2335 | GC, remodel, ADU | Fremont · Alameda County | — | — |
| Oliver & Walker Construction LLC | Phillip Ramoine Oliver | — | (510) 978 7862 | GC, remodel, ADU | Hayward · Alameda County | — | — |
| Oliver Builders INC | Oliver Severin | — | (510) 827 5305 | GC, remodel, ADU | Berkeley · Alameda County | — | — |
| Oliver De Silva INC DBA Gallagher & Burk INC | Matthew Patrick Mascaro | — | (510) 261 0466 | Other | Oakland · Alameda County | — | — |
| Oliver Diamond Construction | Diamond Oliver | — | (415) 596 9979 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| Oliver Gardens LLC | James Longyear Turner | — | (415) 233 0386 | Windows, patio, painters | Oakland · Alameda County | — | — |
| Oliver Heating And Air | Oliver Heating And Air | — | (510) 432 1742 | HVAC | San Lorenzo · Alameda County | — | — |
| Olmedo's Construction INC | Carlos Alberto Olmedo | — | (925) 487 2536 | GC, remodel, ADU | Dublin · Alameda County | — | — |
| Olsen Consulting | Olsen Consulting | — | (510) 329 2373 | GC, remodel, ADU | Castro Valley · Alameda County | — | — |
| Olsen Painting | Olsen Painting | — | (925) 525 0154 | Windows, patio, painters | Pleasanton · Alameda County | — | — |
| Olson And Co Steel | Dylan David Olson | — | (510) 567 2200 | GC, remodel, ADU | San Leandro · Alameda County | — | — |
| Olson Electrical Services | Gregory Lee Olson | — | (415) 606 0671 | Electricians | San Leandro · Alameda County | — | — |
| Olson's Painting Company | Myron Michael Olson | olsonspainting@icloud.com | (510) 521 3351 | Windows, patio, painters | Alameda · Alameda County | — | — |
| Olwin Landscape Design & Construction INC | David Thomas Olwin | — | (925) 462 8153 | GC, remodel, ADU | Pleasanton · Alameda County | — | — |
| Olympic Heating And Air | Olympic Heating And Air | — | (510) 967 1796 | HVAC | Oakland · Alameda County | — | — |
| Om Heating & Air Conditioning INC | Vinodkumar Sumanbhai Patel | — | (510) 845 1090 | HVAC | Berkeley · Alameda County | — | — |
| Om Plumbing Service | Suresh Ramjl Rabadiya | — | (925) 577 6701 | Other | Livermore · Alameda County | — | — |
| Omega Roofing Solutions | John Joseph Burke | — | (925) 599 2233 | Other roofers | Livermore · Alameda County | — | — |
| Omega Termite And Pest Control INC | Allen Glenn Jr Kanady | — | (510) 562 1333 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| Omegan Construction | Felim Thomas Egan | — | (503) 421 0802 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| Omni Mechanical Solutions | Joseph Charles Tenca | — | (925) 218 2340 | HVAC | Livermore · Alameda County | — | — |
| Omnistone Masonry INC | Mario Levak | — | (510) 782 1022 | Other | Hayward · Alameda County | — | — |
| Omr Construction Group Realestate Investment INC | Wilfredo Jose Orozco Martinez | — | (510) 512 3689 | GC, remodel, ADU | San Leandro · Alameda County | — | — |
| On Point Construction | Bruce Wayne Dockter | — | (510) 501 6874 | GC, remodel, ADU | Castro Valley · Alameda County | — | — |
| On R Way Plumbing LLC | John Rudolph Juan | onrwayplumbing@gmail.com | (415) 794 1331 | Other | Hayward · Alameda County | — | — |
| On Site General Engineering INC | Richard John Paul Estrada | brett@weareonsite.com | (888) 233 4167 | Other | Livermore · Alameda County | — | — |
| On The Level Construction | Andrew James Lacroix-snider | — | (510) 213 1556 | GC, remodel, ADU | Alameda · Alameda County | — | — |
| On The Surface Flooring INC | Jake Bippart | — | (510) 728 0336 | Other | Hayward · Alameda County | — | — |
| On Time Builders | On Time Builders | — | (510) 793 7470 | GC, remodel, ADU | Newark · Alameda County | — | — |
| On Top Construction INC | Hayden Charles Homes | — | (925) 485 6133 | GC, remodel, ADU | Livermore · Alameda County | — | — |
| On-site Commercial Services INC | Richard John Paul Estrada | — | (888) 233 4167 | GC, remodel, ADU | Livermore · Alameda County | — | — |
| One - Connection Remodeling And Repairs | Jose Daniel Alfaro Rivera | — | (510) 415 0900 | GC, remodel, ADU | Oakland · Alameda County | — | — |
| One Of The Best Painting | One Of The Best Painting | — | (510) 757 4565 | Windows, patio, painters | Fremont · Alameda County | — | — |
| One Scaffolding INC | Taein Park | — | (510) 534 2290 | Other | San Leandro · Alameda County | — | — |
| One Step Plumbing | One Step Plumbing | — | (510) 682 9075 | Other | Berkeley · Alameda County | — | — |