 | ODD HEIBERG AS | 984556128 | HORTEN |
| ODDMUND GROVEN AS | 923627804 | ØRLAND |
| Odd-Petter Hosen AS | 947714821 | ÅFJORD |
| ODD SMÅGE AS | 954505170 | AUKRA |
| ODD STENSVOLD AS | 995680084 | LARVIK |
| ODDVAR MELING AS | 980151794 | STAVANGER |
| ODDVAR NYBROT AUTORISERT RØRLEGGERFIRMA | 930232882 | BJØRNAFJORDEN |
| ODDVAR ØYGARD AS | 985793581 | ÅL |
| ØDEGAARD ANLEGG AS | 992170905 | BRØNNØY |
| ØDEGAARD OG STERTEN AS | 997907116 | BÆRUM |
| ØDEGÅRD BYGG OG MASKIN AS | 919232773 | LUSTER |
| ØDEGÅRDENS PLANTESKOLE OG UTEMILJØ AS | 983136613 | GRIMSTAD |
| ODIN BRANNTEKNIKK AS | 922957398 | OSLO |
| ODIN BYGG AS | 982592992 | BERGEN |
| ODLAND AS | 914419700 | HÅ |
| O DRAGE ENTREPRENØR AS | 963505329 | SUNNFJORD |
| OEG TEGNEKONTOR AS | 988380717 | TRONDHEIM |
| ØEI AS | 812508032 | OSLO |
| OEN AS | 944328785 | BERGEN |
| ØEN & HAUGSTAD AS | 988008885 | HÅ |
| ØEN HYTTEBYGG AS | 892353662 | HOL |
| ØEN KULDETEKNIKK AS | 980838277 | VOLDA |
| OFOTEN MASKIN AS | 974492032 | NARVIK |
| OFOTEN MEK AS | 924426993 | NARVIK |
| OFOTEN RØR AS | 968277898 | NARVIK |
| ØGLÆND-NORHEIM AS | 990696659 | SANDNES |
| O.HANSEN & SØNNER A/S | 945937513 | KARMØY |
| Ø. HELLESØY RØRLEGGER SERVICE | 990118469 | BERGEN |
| OHNSTAD AS | 923363270 | LARVIK |
| ØIJORD & AANES ENTREPRENØRFORRETNING AS | 957749933 | RANA |
| ØISETH MONTASJE AS | 991391401 | KONGSVINGER |
| ØISTAD ELEKTRO AS | 988277231 | GRAN |
| ØISTEIN ASK ANDERSEN | 970335633 | SANDEFJORD |
| ØIVIND ÅSMANN | 968352113 | ULLENSAKER |
| ØIVIND BRÅTHEN AS | 966890967 | ØVRE EIKER |
| ØIVIND FJELD BYGG OG TØMRERMESTER AS | 982205492 | OSLO |
| ØIVIND LYSTAD AS | 936860478 | KRISTIANSUND |
| O J MILJETEIG AS | 938173605 | HAUGESUND |
| O.J. RØR AS | 998554675 | BÆRUM |
| ØJ RØR AS | 914179165 | KRØDSHERAD |
| OK ANLEGG AS | 912697290 | VÅLER (ØSTFOLD) |
| OK ANLEGGSSERVICE AS | 984797540 | DRAMMEN |
| OK BAD AS | 992779926 | TIME |
| OK BYGG & ANLEGG AS | 928202720 | OVERHALLA |
| OK+ BYGG AS | 933108279 | BERGEN |
| ØK-BYGG AS | 924531215 | GRAN |
| OK ENTREPRENØR AS | 995789418 | ÅLESUND |
| OKER ARKITEKTUR AS | 976186419 | OSLO |
| O K LIE AS | 982049741 | ØVRE EIKER |
| Ø.K MASKINDRIFT AS | 918697365 | ØSTRE TOTEN |